MARK_CONFIRMED only when Zero balance

We're using iMIS Version 10.5.

I'm trying to generate confirmation letters (via Generate Reports) only when there is a zero balance.

I want to restrict printing only to those records for which a confirmation letter has not been printed (by marking the record), but want to keep the option of reprinting all if necessary (include confirmed).

I created a custom Crystal (Version 9.2) report that I would like to test for the mark. I which table is this "mark" stored?

Could I, instead, conditionally apply the MARK_CONFIRMED option?

Thanks.