Agreed that the exact meaning of a diversion depends on the state, and thus, whether it would count as a "conviction" which was expunged from the FAA's perspective. The OP made a number of statements which suggest that in Tennessee it may not have counted as a conviction at the time, though there is still some confusion here: Evidently AOPA legal counsel advised he disclose it in any case. Certainly the conservative thing to do if you don't want to be the test case. OTOH, that may have been unnecessary if in TN at the time the judicial diversion was not legally a conviction. Unfortunately, in these type of cases, there is often no clear answer.