TWOK was more indiscriminate than just trying to pretend on some level that TMP never happened. TWOK blew right into TOS and bulldozed anything that stood in its way. It put Chekov aboard ship during Space Seed
and inserted yet another serious love interest into Kirk's past with a crowbar, just for starters.
TWOK, even more than TMP (with its valiant but ultimately futile attempt to retcon Klingon appearance), tried to unburden itself of the continuity porn that would eventually sink the Prime Universe part of the franchise.
I've seen prints where it's just "STAR TREK: THE WRATH OF KHAN." Too, there's promotional artwork and images that did not have the "II" yet.
I was in high school when TWOK was released. Originally, there was no "II" in the title. That was added in a later release, and everybody noticed. It's wrong to say it was originally "omitted" (ETA:
not directed at 00
, someone else said that). It was simply absent.