Customs wants a declaration that matches the cargo. Your buyer’s bank wants a document set that matches the letter of credit, to the letter. These are different tests and passing one does not pass the other.
Banks reject on discrepancies that have nothing to do with the goods: a description that does not match the LC wording exactly, a late presentation, a missing endorsement, an on-board notation in the wrong place. Each rejection costs you the discrepancy fee and, more expensively, the time.
We check the export set against the LC terms before it goes to the bank. It is the cheapest checking anyone will ever do for you.