Vacbear, from what I know of the Hoover in the 1970s, there were endless models in the freedom ranges, although I have to say I only every really saw the basic models in red, orange/cream, and green/cream, with electronic in orange or cream. But there were also two styles of electronic models, and variations in lilac too.
I know that as the 1970's drew to a close the Freedom cleaners were streamlined into red and cream, but as you've said there was also the constellation, two celebrity models, plus the standard basic cylinder (was it 419?). Hoover dropped the red Freedom cleaner around 1984 to replace it with the Powerglide, a cleaner which sported the same dustbag and identical motor. All that was different was the footprint of the cleaner as it was not quite so long in shape. But quite why this was done or where the cleaner fitted in along the Compact models, I just do not know. One thing which Hoover could be relied upon was providing plenty of choice, because as you also say, there were many exclusive models available too, as well as older lines still in stock (even possibly in production) after the replacement model had been launched.