In Issue 18 (December 1978) of Starlog there is an interview with Star Wars producer Gary Kurtz that talks about The Empire Strikes Back. I thought this section of the article was rather amusing:I just watched the interview circa 2010 where gary Kurtz addressed that.
They had an outline for more than one movie...but Lucas and fox thought it would flop so they took the idea of franchise off the table for practical purposes and “Star Wars” scrolled on the scream without an episode.
The fox executives also said 4 would be too confusing and would make what looked like a long shot movie even more of a Head scratcher.
Going along with this long-range concept, the producer refuses to taint the new production with the usual Hollywood sequel slang. The film, for instance, is never referred to in Lucas-Kurtz circles as Star Wars II. "I would never call it that," Kurtz winces. "Our working title is The Empire Strikes Back. And as I said, it's part of a plan that George and I had from the inception of the original film. What we wanted to do was to relate every subsequent Star Wars adventure as an episode of a continuing story, like the old movie serials used to do. We were going to call this movie Star Wars Episode Two: The Empire Strikes Back, but we ran into some problems. You see, although this story is a direct sequel to the first movie, we have three more stories that we eventually want to film that actually occur before the point where the first Star Wars begins.
"So we've been toying with the idea of ignoring the numbers completely. Instead, we'll give each movie episode a unique title. I mean, if we had to give each film its true number in the series, this movie would be called Episode Five: The Empire Strikes Back. The first film would be called Episode Four! Can you imagine how complicated it would get? If we released a story like that publicly through a press release, thousands of people would be totally con- fused. Everyone would want to know what happened to the other three movies."