"Nope. I saw it in November '66 and that prologue was definitely played."
Are you saying specifically that what you remember hearing played when you saw the show in '66 was the brief prologue -- i.e., "Hello, Dolly!" -- as heard on the original cast album with Carol Channing? That is rather surprising.
When I saw the show at the end of the run, with Merman, there was no prologue or overture whatsoever. The music that leads into "Call on Dolly!" started, the curtain went up, and we were off!