ST II vs ST III Battle Damage

[Qonundrum]

I thought the long held fan theory was that the ship had another battle in between movies. Maybe that's connected to DC comics or something that inspired those stories.

Ditto. I like to believe there was another off-screen battle after Spock's coffin with Klingons, which helps (a) explain the damage and (b) the build-up with the Klingon arc.