Thread:HumansCanWinElves/@comment-9605025-20201115165902/@comment-45117243-20201115211428

Hmmm looks like you are right. The migrated pages are no longer on the Contribution page nor on the Special:Prefixindex list.

I tried to investigate it further and it was hard. It seems like migrated board comments weren't deleted, but then maybe it's about wall messages. On the migrated wikis I'm active on no wall threads have been migrated yet. I tried checking some random wikis, but it looks like many switched to talk pages.

Finally I found a migrated thread which exists also on the original pages:
 * https://the-universe-of-the-universe.fandom.com/wiki/Message_Wall:Animator_Of_Awesomness?threadId=4400000000000001054
 * https://the-universe-of-the-universe.fandom.com/wiki/Special:PrefixIndex/Thread:Animator_Of_Awesomness/@comment-34407532-20191030231755

So at least it's not always the case...