* you reserve space and possibly set an original value with "hshsiz DB 100" or "paraml DB ?"
* assignment is a different business which involves a runtime instruction (MOV)
Hence the same difference (no = sign for the first, passive, compile-time operation; an = sign for the second, active, runtime operation) in this proto-C.
(Of course, this doesn't answer your question of "when" did the syntax of those 2 operation fuse :-) )