Why unused CCITT #2 codes [telecom]

Bill asked:

There are 32 combinations of bits available from a 5-unit code such as

Baudot/Murray. They weren't all used, though, at least in the CCITT #2
> alphabet, and I'd like to know why.
>
> Bill

The book *Principles of Telegraphy (Teletypewriter) *at

states that three codes in CCITT Alphabet #2 are unassigned. Figures case (shifted) F, G, and H are described as "Unassigned internationally, may be used with local meanings in national systems." Figure C-2 shows them as !, & and STOP in the "U.S. Military Communication Alphabet."

Chuck