I didn't know that about the file extension. I don't see anything about that anywhere. The only thing I could find on this issue was here:
https://forums.cncnet.org/index.php?topic=4261.0
The guy even says that they are ymr, so that's what I made all of them. Sure enough, making them map fixed it for most of them but I can figure out the rest.
Thanks for the fast response!