I accidentally started gimbal calibration with the gimbal stabilizer still on, so it couldn't move at all. Apart from the gimbal not being level for that flight, would this have caused long term damage?
I've done this. Powered up, noticed the camera wasn't dancing, soiled myself then quickly powered down. I've had 6 or 7 full flights since then. Not a single issue to report....so I think you're good. (That said, I'm sure doing this 20 times would probably not be a good thing.)
I do a gimbal calibration every new battery flight. It's quick...and it makes me feel better.