Thank you, Reymond, but you've identified the exact problem I am having.  ALL estimates continue to show an open balance even when the full amounts HAVE BEEN converted to invoices.  I understand that these amounts should zero out (or be reduced) when an invoice is created, but that is not happening.  Not a single estimate that I've ever created shows a reduced/zero open balance.  According to what I understand from your answer, this is not correct and doesn't seem like an issue of customizing a report.

Is there a setting somewhere that I need to check?