C.E. Evans wrote:
For all we know, the original Yorktown captain and crew were reassigned to a new Excelsior-class ship with that name.
Doesn't really make a lot of sense based on the reaction of Kirk's senior staff upon seeing it. If they were already in production there would be nothing special about that ship to elicit that response. Prior to The Wrath of Khan
they all seemed to be stationed on or near Earth except for Chekov.
The whole project was probably top-secret until Starfleet needed an actual port for the trial runs.