Originally posted by Grandaddypurple:

Hmm really? I'm pretty sure to notice they didn't respawn
Hitting copper nodes attract mobs from very far away (and I know that for a fact as I had a mining area a couple hundreds meters away from a swamp, and would get swamp mobs checking the area).
If I'm not wrong and guarding skeletons don't respawn, what most likely happened is that it attracted skeletons from another area, e.g another burial chamber or a ruined tower

I have never seen burial chamber or tower skeletons respawn. I think you're right, it's more likely that they wandered in from somewhere else.