The Catalyst wasn’t a thing until the very last season, so there was nothing to lock, because there was no season after that.
There hasn’t been word on whether or not we’ll be able to use the Catalyst for old season tier transmog or not. At least, not that I’ve been able to find.
Editing and adding that I did link the official announcement about this in post #22, but I’ll also add it here now that we have word: