Re: Constitution, Miranda, and Constelation Class
This is speculation. In one of the mission orders for the Atlantis, there is a diagram of an Excelsior-class starship. It's possible that the two may be connected. If so, it may partly explain why this class of ship is so prominent. The registry of this ship is NCC-72007, which might imply that Excelsiors were still being built in the 2350s and 2360s.
My not-in-any-way-canonical take on the seemingly inappropriate high registration numbers is that a)Starfleet keeps a number of older vessels mothballed, b)SF refits them when a temporary need for more ships arises, and c) many of the numbers represent reactivated Excelsior hulls in which the original names have passed on to newer vessels.
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