How to investigate discrepancies in month-end prepaid expense amortization?

When I first took over month-end close for a small company, I encountered an often underestimated issue: the amortization schedule for prepaid insurance expenses didn't match the GL balance, and the boss only noticed that profits had suddenly spiked. It wasn't the kind of error where the cause is obvious at a glance; it was more like several small oversights compounding together. I started by…