...in the text scroll at the beginning of the film--mention the episode or subtitle. All of that was added after "Empire Strikes Back" was released.
That has always bothered me too. When it was released I think I saw it 14 times. We really didn't have that much else to do as kids at the time on Friday and Saturday nights, so we might see it three times in a day just to hang out with friends and find little details in the film to make fun of or appreciate. It was a good time, and it only cost like $2 to get in. Going to the arcade was way more expensive and you had to stand up the whole time.
But it was NEVER EVER called anything other than "Star Wars".
I never actually understood why they felt the need to add the "Episode IV" BS to begin with--or include the idiotic edits that George Lucas added in later.
Also, I think there is one other huge tell that is still in the movie that--to your point--the whole series was made up after the fact of the original "Star Wars" script that always bothered me: when we are first introduced to Ben Kenobi and he is told by Luke that R2-D2, "claims to be the property of an Obi-Wan Kenobi," which clearly--through both the musical score and facial expression--is a shock to Ben Kenobi. He then goes on the say, "I don't seem to ever remember owning a droid. Very interesting."
This made perfect sense in the original movie since R2-D2 was sent by Princess Leia and there was no reason for him to be familiar with R2. But with the prequels as context that whole line of reasoning is left mute. And yes, people have bent themselves into all sorts of logical pretzels to explain this blatant lack of continuity, but it is very hard to support those claims based on the original film. The claim that all of this was already thought out beforehand just falls flat IMO. Lucas caught lightning in a bottle and ran with it--albeit in a bit of a sloppy way from the story standpoint IMO.
There are plenty of other plot holes in the entire series, but that one is the one that tells me just how much of this story was made up on-the-fly.
Now I'm off to find my copy of that original score and throw it on the turntable. For all the money they spent on special effects, "Star Wars" would not be the film it was without the brilliant score by John Williams. It is worth listening to all by itself.