There are several reasons why a 1994 won't learn from an oem remote, most of which doesn't mean the 1994 is "broken". If it learns other signals, it certainly isn't.
Doesn't the 1925 also have the 6 pin header? If so, JP-1 could look at the modem download you got from RS/UEIC and you could build a similar one with KM and upload it to the 1994. I suspect they may have included a protocol upgrade as well, and that'd be interesting to look at on it's own merits.
Jim