Well, for the returning "nemesis", IMC, it depends on the amount of time that has lapsed. Turning undead is the most common cause of "recurring" enemies, but there are many other causes that can have similar effects (for instance
greater command, and the like). The key to the issue is whether it was a) a significant challenge, b) has enough time/space passed as to be reasonably considered as a seperate encounter c) was the challenge really overcome?
When you encounter the same undead within the hour, well, I'm afraid you haven't then really overcome the challenge: no xp for turning them. (
IIRC, FWIW, in 1e, you only got xp for destroying undead, not turning them). Same goes for the leiutenant whom you commanded to
flee. If they return and are still itching to kick your posterior; you didn't overcome the challenge. If they flee the complex, and two weeks later confront you in your local pub with a band of hooligans, then I'd say yes, you overcome the earlier challenge.
As for the bat swarm, I'm failing to see why the rest of the team should gain XP.