[Bilgepump]

If you are at the point where you need to capture the Black Pearl, and you help someone else finish their quest, your quest will be marked complete, even if you are not the one who initiated the final battle.

I finished mine last night. My wife was helping, and she was at the final stage, too. When we finished, hers was also marked complete, even though I was the one that initiated it.

This is not necessarily a bad thing, but it's something you should be aware of.