"Are you willing to help us overpower the Romulan B-type Warbirds we may encounter? Are you prepared to help us detect them through their cloaking shields? You see my problem, Admiral."
- Captain Jean-Luc Picard to Romulan Admiral Alidar Jarok, 2366
Picard later refers to the "Warbird Class starship", presumably the Federation designation of the D'Deridex Class. On this and, as I recall, another occasion on screen (but not this), spacecraft were referred to not just by class, but with an additional letter designator, suggesting subtypes. I don't think we need a huge taxonomic heirarchy here, but the simple fact is that the Enterprise-B, for instance, would thus seem to be a B-Type Excelsior (conveniently). The Enterprise refit and 1701-A would be a B-type (or perhaps C-type or D-type) Constitution.
There's more than just this, though . . . including some surprises.