How to handle a situation where a correctly issued Purchase Confirmation was mistakenly modified

We are an exporter, and we ship purchased goods in the same month they are acquired. We issue the Purchase Confirmation to our suppliers as of the last day of the month in which the shipment occurs, and the supplier issues a zero-rated tax invoice using the Purchase Confirmation issuance date. Regarding a specific month's purchase (e.g., October of last year), we issued the Purchase Confirmation as of the last day of that month, and the supplier also issued the zero-rated tax invoice accordingly. However, when issuing the Purchase Confirmation for the following month, we belatedly discovered that the previous Purchase Confirmation was transmitted as a 'modification' due to an error (e.g., the initial new amount was subsequently transmitted as a modified, larger amount). We have only realized this now, after the VAT filing period has passed. If we correct the amount on the modified Purchase Confirmation, the issuance date shifts to several months later. We are concerned that if the issuance date is pushed back, the zero-rated tax invoice for the original month might not be recognized. We would like to inquire how we should handle this situation.