It’s interesting that SW’s “glory days” lasted only three years.
As of May 24th, 1983, there were only two Star Wars films. So if you’re saying the “glory days” are the years in which only Star Wars and/or Empire existed, that’s six years (1977-1983). That’s if I understand your intent correctly. If you intended to say Empire sucked all the glory out of the franchise, then you just go right ahead saying three years.