For the record, AP invoice entry does not allow /c fields ala SO and PO entry.  I enter AP invoices without any line values as a record of filing taxes at month end.  I enter the invoice and use the header comment filed to record the filing confirmation number.  This provides a quick way to verify (at a later date) that the filing was completed.  I use the default gl account for the vendor, zero amount.  The header comment defaults to the line comment field.  I find this an ideal way to track.

For the record, AP invoice entry does not allow /c fields ala SO and PO entry.  I enter AP invoices without any line values as a record of filing taxes at month end.  I enter the invoice and use the header comment filed to record the filing confirmation number.  This provides a quick way to verify (at a later date) that the filing was completed.  I use the default gl account for the vendor, zero amount.  The header comment defaults to the line comment field.  I find this an ideal way to track.