Wow, my ability to search Google is horrible. =/
I was searching with all these stupid queries before posting this, and after I posted, I had the bright idea to search "tm m9a1 slide does not fit on kjw" and this is the first link that pops up:
Tokyo Marui M9A1 (No Discussion) - boards.ie
A brief skimming shows that it is indeed a redesign, and no longer compatible with previous body kits.
So I guess I answered my own question. Sorry guys. Hopefully the thread will at least be here to answer the question for someone else.