So, off to the source. Inside msg.h I found a more complete token list, though it seems there are tokens listed in token.txt that aren't in msg.h - like token BX for SVSJOIN. How odd.
For now I'm tossing aside the idea of using tokens in the script I'm modifing (POE::Component::IRC::Service::Unreal32 was something I needed and didn't exist, so I'm adjusting ::P10 and ::Hybrid's modules to cover it), for lack of certainty on which tokens to follow. I figured I'd at least inquire as to why the two lists are different, or perhaps nudge someone to bring the two back in sync...