IIRC, regardless of a true-up provision, if it is found that there was an error in calculating the Match, the plan administrator must "true-up" all participants. In these cases, though, it's a correction as opposed to a true-up, although the process is the same.
legort69:
This is completely off-topic, and I can't quite tell from your description, but I am always suspicious when some limit relating to deferrals applies with respect to the 401(a)(17) limit on compensation that the plan is, shall we say, not optimally designed because of a misconception about how the 401(a) (17) limit operates.