Tax & VAT Compliance 2026-11-04 Editorial Team at ammex.org.mx

SCCCyG Over-Discharges (Sobredescargos), UMT Conversion Errors & `R1` Rectifications

In a Mexican IMMEX plant operating under IVA/IEPS Certification, two technical systems must stay mathematically synchronized every month:

Your internal Anexo 24 system, which tracks inventory in physical quantities (UMT: Kilograms, Pieces, Square Meters) linked to specific part numbers and Bills of Materials (BOMs).
SAT’s external SCCCyG (Anexo 30/31) portal, which ignores part numbers and physical quantities entirely and tracks your 16% VAT credit exclusively in Mexican Pesos (Valor Comercial MXN) grouped by 8-digit tariff fraction (Fracción Arancelaria).

When the mathematical bridge between UMC (your ERP unit), UMT (the customs tariff unit), and MXN (the commercial value in pesos) breaks down, your compliance team confronts three operational emergencies: Over-Discharges (Sobredescargos), Phantom Open Balances (Saldos Abiertos), and Rejected Discharge Reports (Informes de Descargo No Válidos).

1. Anatomy of an Over-Discharge (Sobredescargo) vs. a Phantom Open Balance

When your Anexo 24 software runs its monthly FIFO (PEPS) consumption engine to generate the pipe-delimited .txt Discharge Report for SCCCyG, it converts the quantity of raw materials consumed in exported finished goods into a Commercial Value in Mexican Pesos (MXN) using this formula for each temporary import lot (IN or V1):

MXN Value Discharged = Lot Commercial Value (MXN)
                       × (UMT Quantity Consumed by Export BOM ÷ Total Lot UMT Quantity on Import Pedimento)

Now see what happens when the UMT-to-UMC Conversion Factor in your Anexo 24 catalog diverges from the actual weight declared by the customs broker on Table 551 of the import pedimento:

Error Direction	Mathematical Cause in Anexo 24	Impact on Anexo 24 & SCCCyG (Anexo 30/31)
*1. Over-Discharge (Sobredescargo)*	Your BOM / conversion factor deducts more `UMT` (e.g., `1.25 Kg` of resin per housing) than the actual net weight declared per unit on the `IN` pedimento (`1.00 Kg`).	Premature Credit Exhaustion: Exporting 800 housings consumes all `1,000 Kg` (100% of the `$ MXN` credit in SCCCyG). When you export the remaining 200 housings on the floor, your Anexo 24 either cannibalizes newer `IN` pedimentos ahead of schedule or attempts to report a `$ MXN` discharge that exceeds the total credit balance available in that tariff fraction in SCCCyG.
*2. Under-Discharge (Subdescargo* / Phantom Open Balance)**	Your BOM / conversion factor deducts less `UMT` (e.g., `0.010 Kg` per bolt) than the weight declared by the broker on the `IN` pedimento (`0.014 Kg` per bolt).	Stranded Expired Credits: After 100% of the physical bolts have been assembled and exported (`0 pieces` left in SAP and on warehouse shelves), 28.5% of the `Kg` and 28.5% of the `$ MXN` VAT credit remain open inside SCCCyG. At Month 18 (or Month 6 for `V1`), that phantom balance turns into an *Expired Credit (Crédito Vencido)* demanding cash tax and surcharges.

2. The 4 Root Causes of UMC-to-UMT Conversion Drift

Why do conversion factors fail in nearly every manufacturing plant that has not audited its master catalog?

Broker Gross-Weight Proration at the Border: Your ERP buys steel screws (7318.15.99) by the Piece (UMC = 06), while the Mexican tariff (TIGIE) requires Kilograms (UMT = 01). Instead of multiplying the piece count by the engineering net weight per screw, the customs broker’s clerk prorates the gross pallet weight (including wooden skids and cardboard gaylords!) across the invoice lines. You end up declaring 400 Kg of wooden pallets as “temporary imported steel screws” on Table 551, weight that your engineering BOM will never discharge!
Static Catalog Factors Applied to Variable-Weight Lots: Steel coils, copper wire spools, plastic rolls, and chemical drums vary by ±3% to 6% in net weight from lot to lot. If your Anexo 24 software uses a single static conversion factor in the Material Master instead of a Dynamic Lot Conversion Factor (Lot UMT ÷ Lot UMC per pedimento line), every single shipment leaves a positive or negative residual in SCCCyG.
Decimal Truncation (2 vs. 6 Decimals): Converting US Pounds (LB) to Kilograms (KG) using 0.45 instead of 0.453592 creates a 359.20 Kg phantom balance on every 100,000 lbs imported.
Tariff Reclassification Midway Through a Lot’s Life: The customs broker imported a component under fraction 3926.90.99 (UMT: Kg) from January to June, and then reclassified the exact same part number to 8538.90.99 (UMT: Piece) in July without splitting the part number or updating the Anexo 24 tariff-fraction mapping.

3. Why SAT Rejects SCCCyG Reports as “No Válido” (Invalid) & How to Fix Each Error

When you upload your monthly or bimonthly .txt Discharge Report to the SAT SCCCyG portal, the system returns a processing receipt (Acuse). If the status is No Válido (or individual lines are rejected), diagnose the error against this table:

SCCCyG Rejection Cause	Why SAT’s Validator Flagged It	Exact Technical Fix
1. Return Pedimento Not Found in SAAI (`Pedimento de retorno inexistente o no modulado`)	Your `.txt` file includes a consolidated `RT` or virtual `V1` pedimento that was created in late March, but the broker did not actually close and pay/modulate it at customs until April 3rd.	Remove the April-modulated pedimento from the March discharge report (include it in the April report) and re-upload within your remaining replacement attempts.
2. Tariff Fraction Has Zero Initial Credit (`Fracción arancelaria sin saldo de crédito`)	Your Anexo 24 BOM discharged a component under fraction `7326.90.99`, but on the original `IN` pedimento the broker actually declared `7318.15.99` (or paid the VAT in cash `FP 0` instead of `FP 21`).	Cross-check Data Stage Tables `551` and `557`. Re-align the part number’s tariff fraction in Anexo 24 to match the actual `IN` pedimento (and exclude `FP 0` cash-paid lines from the SCCCyG `.txt` report).
3. Syntax / Pipe-Delimiter / Decimal Error in `.txt` File	Extra spaces, thousand-separator commas (`$1,200.00` instead of `1200.00`), wrong date format, or missing pipe (`	`) in the ASCII structure required by the SCCCyG manual.
4. Discharge Value Exceeds Open Credit in Period (`Valor descargado mayor al crédito disponible`)	Classic *Over-Discharge (Sobredescargo)*: your report tries to deduct `$5,200,000 MXN` from the `2025-08` credit pool of fraction `8542.31.99`, which only has `$4,900,000 MXN` open.	Audit the UMT conversion factor and BOM consumption for that fraction, cap the lot discharge at 100.00% of the lot’s original `Valor Comercial MXN`, and re-run FIFO.

4. When and How to File an `R1` Pedimento Rectification (Article 89 Customs Law & RGCE Rule 6.1.1)

If your audit reveals that the error is not inside your ERP or BOM, but was committed by the customs broker on the pedimento itself (for example, the broker typed 15,000 Kg instead of 1,500 Kg in Table 551, declared the wrong tariff fraction, or forgot to declare an RT export return cleanly), editing your internal Anexo 24 software will not fix SAT’s SCCCyG database.

To change SAT’s official record, you must file a Rectification Pedimento (Clave R1) under Article 89 of the Mexican Customs Law and RGCE Rule 6.1.1:

Critical Rules for `R1` Rectifications in IMMEX Operations:

When You Can Rectify Automatically vs. When You Need Prior AGACE Authorization (Rule 6.1.1):
- Under Article 89 of the Customs Law, importers can generally rectify pedimento data any number of times before or after customs clearance (provided the automated selection mechanism is not currently executing an inspection and SAT has not initiated a formal audit).
- HOWEVER, under RGCE Rule 6.1.1, if the R1 rectification generates a favorable balance (saldo a favor), reduces taxes paid, changes the importer’s RFC, changes the customs regime, or alters specific regulated fields/fractions, the customs broker cannot validate the R1 directly unless the company first submits a formal application and obtains a prior written authorization resolution from AGACE!
Rectifying an Import Pedimento (IN / AF / V1) vs. an Export Pedimento (RT):
- When an R1 on an IN import pedimento is validated and paid in SAAI, SAT’s nightly/weekly batch sync updates the corresponding entry in your SCCCyG Statement of Account.
- When an R1 on an RT export pedimento is paid (for instance, correcting the commercial value or operation key), you must wait 48–72 hours for SAAI to register the R1 and then transmit a Replacement or Correction Discharge Report (Informe de Descargo de Corrección) in SCCCyG referencing the R1 pedimento number.

Frequently asked questions

What is an over-discharge (sobredescargo) in Mexico's SCCCyG (Anexo 30/31)?

An over-discharge (sobredescargo) occurs when the monthly or bimonthly Discharge Report (.txt file) generated by your Anexo 24 software attempts to deduct a higher commercial value in Mexican pesos (MXN) for a specific 8-digit tariff fraction than the actual available credit balance recorded for that tariff fraction inside SAT's SCCCyG (Anexo 30/31) ledger, or when you discharge 100% of the commercial value of a lot before all physical units have been exported.

Why does SAT's SCCCyG portal reject a Discharge Report as 'No Válido' (Invalid)?

SAT's SCCCyG validator rejects a .txt Discharge Report as 'No Válido' (or 'Validación con Errores') for five main technical reasons: 1) Formatting or pipe-delimiter syntax errors in the .txt layout; 2) Referencing an export or return pedimento (RT, V1, F4) that does not yet appear as 'paid/modulated' in SAT's SAAI database for that period; 3) Declaring an 8-digit tariff fraction on the discharge line that never opened a Forma de Pago 21 credit in the statement of account; 4) Submitting an Ordinary Report outside the allowed statutory calendar window; or 5) Exceeding the maximum allowed replacements for an ordinary report.

How does a UMC-to-UMT unit conversion error cause phantom open balances or over-discharges?

Your ERP consumes components in Commercial/Engineering Units (UMC, such as Pieces, Feet, or Rolls), whereas SAT's pedimento Table 551 and Anexo 24 track customs balances in Tariff Units (UMT from Appendix 7 of Anexo 22, most commonly Kilograms '01' or Square Meters '04'). If the broker declares a net weight of 1,260 Kg for 100,000 screws on the IN pedimento (0.0126 Kg/piece), but your Anexo 24 catalog uses a static conversion factor of 0.0120 Kg/piece, exporting all 100,000 screws will only discharge 1,200 Kg ($190,476 MXN), leaving 60 Kg ($9,524 MXN) stranded as a phantom open balance in SCCCyG.

When do we need an R1 Rectification Pedimento (Article 89 Customs Law & Rule 6.1.1)?

Whenever the root cause of an Anexo 24 or SCCCyG mismatch is an error on the pedimento itself, such as a wrong 8-digit tariff fraction, a 10x typo in the UMT quantity (e.g., declaring 5,000 Kg instead of 500 Kg), an omitted 'CI' or 'FP 21' identifier, or an incorrect commercial value, changing your internal Anexo 24 database will not fix SAT's ledger. You must file an R1 Rectification Pedimento so that SAT's SAAI / Data Stage database updates the official record.

Does filing an R1 rectification automatically update our SCCCyG (Anexo 30/31) statement of account?

On an import pedimento (IN, AF, V1), once the R1 rectification is validated and paid in SAAI (and provided any required AGACE authorization under Rule 6.1.1 is obtained), SAT's SCCCyG batch process updates the credit balance within several business days. On an export return pedimento (RT or V1 export), after paying the R1 rectification, you must also transmit a Replacement or Correction Discharge Report (.txt) in the SCCCyG portal so the credit deduction reflects the rectified figures.

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