I have a few hundred tracks spread across several non-exclusive sites. I’ve been doing this for about 8 years.
I recently saw a “negative balance” in my ProductionTrax account and inquired about it. According to them, an accounting error from TWO YEARS earlier, which they never communicated to me until I brought it to their attention. (In my view, if this is their error, they should eat the cost.)
My advice is to keep good records of 1) what was sold, 2) what was paid, and 3) whether cue sheets were submitted for them (if you have a PRO). It won’t prevent errors on their part or change bad policy but at least you’ll know which sales are in question.