Well, I can tell you how I view the incident.
The Excalibur was wrecked, not destroyed. Hence Chekov's line "The Excalibur...looks dead sir."
Now Internal politics of the Federation, since Roddenberry made the parrallel to the United States, would not tolerate the loss of a multi-billion (trillion) credit Starship to a "Wargame". Therefore, the entire Incident would be covered up with a thick layer of red tape, and the Excailbur would be towed to a classified facility to recieve a refit. Possibly when the CC refit was introduced. The dead crew, on all ships, but mostly on the Lexington and the Excailbur, would be shifted around to other borders, where they will officially "die" in a raid, or a border skirmish with the said enemy. Also, since the Lexington was also shot up during the battle, it would probably be the first ship to recieve the CC refit, since there was a lot less work to be done on the Lexington than there was on the Excalibur.
That's my take, I think it explains why the 1703 Lexington and 1705 Excalibur are CCs but why 1707 Hood and 1711 Potemkin are only CAs in SFC I.