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". It was simply absent.
An astute point. It's possible, however, that someone who saw the post-release advertising and the posters just outside the theater (all of which would have used the "II") and then saw a "II"-less title on the big screen, synchronized with the first grand statement of Mr. Horner's main theme - well, such a person might think in terms of "omitted."
(As I've mentioned in some old thread: I recall seeing a four-page color spread in one of the Time Inc. magazines just before the movie opened in May 1982 - probably Time
- that featured art and photos from the movie and definitely did not use the "II".)