Is what I'm guessing?
As per this ad:
YUP...
And a most interesting "illustration" (i.e. AD) which clarifies that BULOVA also used alpha (A- E?) denotations to differentiate the variations, on popular selling models... And bear in mind that this was for most model names, sometimes even BY YEAR!
So depending on salability... that might mean the same "President," for instance... sold well for several suceeding years, in 4- 5 variations! Or that a reasonably popular model(s) sold well when introduced, but not necessarily well enough to warrant making say 3- 5 dial+ variants, so it was again reduced to perhaps only the single model "namesake?"
Then others were only released for a year or two as a single model... But then popular model namesakes from competitors were also routinely used and reused (from decade to decade+) by almost every US manufacturer! (Hence the confusion... especially with similar cases, bezels and/or crystals!)
:-) Scott