They inserted transactions for corrections of discrepancies where you could not see they were authored by them; it was just assumed the postmaster did.

They did not let postmasters know about this; probably an order by the post office.

These corrections where incorrect, and caused discrepancies to increase; they mixed plus and minus sign quite often.

They added lines of code to the system running on the counter in the local post office.

They used the message store system like wild west without defining a data schema.