In 1981-1998, it did say Episode IV in the crawl, but nobody thought "I missed I-III. Back to the video store to look for I."
Actually I didn't think exactly that, but in 1980, Star Wars was clearly Episode I, and they skipped over three episode numbers when they released Empire as Episode V.
I remember excited conversations with my friends in school about what must have happened in those missing three episodes (in this case, 2, 3, and 4)--there was a hint of something that happened on Ord Mantell, so clearly there was something juicy in there. Would it come out in a future film? TV series? Who knew? Either way, LOTS of us believed it, until 1981, or maybe later if we didn't see Star Wars again right away. Finding out Star Wars was Episode IV and not Episode I like everyone assumed was kind of anticlimactic. Not as much as the actual prequels, but still a little disappointing.