I think I’ve mentioned before, but as someone who saw it in 1980, it was confusing/unexpected. Clearly Star Wars also dropped you into the middle of the action, but the crawl provided backstory to ease the transition – you knew who the good guys and bad guys were, why they were being chased, and so on. And the beginning of Empire largely followed the same formula. But this was different – the episode number ADDED to the things you didn’t know as the story unfolded. Now you know you’ve missed three of the preceding episodes.
In the end, kids made it work. Clearly a lot of action happened between Star Wars and Empire – Luke becomes a commander, there’s some sort of adventure on Ord Mantell, the Empire regroups, and so on. So retroactively, it became obvious that the three missing episodes were meant to cover all the action between Star Wars, which was obviously Episode I, and Empire, which was Episode V. We didn’t really expect the missing episodes to be filled in by Lucasfilm, so we just made up “Episode III: Rendezvous at Ord Mantell” and stuff like that. We figured the next movie would be called “Episode IX: Revenge of the Jedi” or something and the episode gaps would be designed for us to play around with in our own imaginations.
Which was actually a very cool and weirdly postmodern idea for a bunch of seven year olds to grapple with!
And then a year later, Star Wars got retrofitted with Episode IV, although many of us never learned about that until it came out on home video even later. But by then, our canon was already set: Star Wars would be Episode I forever, and then there was a bunch of “action figures in the backyard” adventures, and then came Episode V. By the time an official Episode IV rolled out, we didn’t need it – we already had our own by then.
And I’m glad they never filled in those missing episodes (kindof like I’m glad they never made any sequels to The Matrix), because there’s no way they could have measured up to what a crew of seven-year-olds came up with. Partially due to the fact that the head kept popping off my Luke action figure, so every episode involved a tragic beheading.