1) Is it worth no longer sharing the same lookup table? My supposition is that this wouldn't practically matter in the modern bloated environment anyway, but it's still annoying and might be a source of additional bugs.

2) Which 4 characters would be skipped for what reason?

I'd initially propose not including: non-printing character space (b45[36]), possible variable wildcard dollar-sign (also a currency symbol that might get translated) (b45[37]), html escape and database wildcard percent (b45[38]), then typical wildcard asterisk (star) (b45[39]). Thus the sequence string would be.

b41 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ+-./:";