Maybe it is still bugged yeah. All the systems (62) that would trigger the bug before 1.105 have been sold without a problem in my case after the fix.
As the fix is not retroactive, you can't tell if a system has been discovered or not when you enter it the first time. If there's no retroactive fix planned, this will be a major pain to explore.
But as 1.1 showed, there is a datestamp on the discovered body. If not they couldn't apply the whole first discovery thing to systems scanned before 1.1. So there maybe hope. Or not if the datestamp is created on sell.
Seems to me that you don't need a datestamp to tidy up the vast majority of this. Problems would only arise where another CMDR has come along before the fix.
E: D knows what objects you have scanned, otherwise the system view would not work. If there are any objects that you have scanned that do not have a discovered tag, then they know there may be a problem (of course, you could have just scanned it recently and not attempted to sell yet). If you have the discovery tag on other objects in the system, then it is a fair bet that there is a problem and you actually discovered the other objects that you scanned. Not perfect, but I bet it would solve 95%+ of the issues, and thus be much better than doing nothing.
Of course, this all presupposes that they have actually found and fixed the bug going forward. The description in the 1.1.05 release notes was sufficiently vague (and said 'rare' whereas this problem is obviously very common), that we do no know if it was meant to be a fix to this problem or not. It may be that they fixed (or thought they fixed) quite another problem where there was no simple way to sort out the mess.