While I don't think we should encourage people necro-ing old threads for the fun of it, I don't think we should have an issue with it, even if it is necroing the last thread on the board, when a reply on topic is made.
At least when it is not purposely to cause trouble.
For linked reply, I see user got a warning, but I think the reply wasn't out of line.
For the record, can moderation read the final post and react only if it is out of line?
Or you can correct me if I'm wrong here.