They were originally different but retconned to be the same character at the end I believe: https://www.reddit.com/r/lotr/comments/9ie9ka/two_glorfindel...

Ah, it seems I need to read deeper. Thanks for clarifying :)

Elves could be released from the Halls of Mandos and reincarnated. It wasn't totally common, but it happened in the Tolkien's world more than once.

There is, for example, a remark in The Silmarillion that "Finrod walks with Finarfin his father beneath the trees in Eldamar". Finrod was killed in Sauron's captivity in Middle Earth.

It could be fairly common, but they would be reincarnated in Aman where Mandos is and thus would have to have sailed back to Middle Earth in order to show up in the stories. There’s just not a lot of traffic going in that direction by the the Third Age.

Yes, we do not really know what was the norm in Aman.

The Kinslaying was considered a great crime, though, which indicates that the murdered Teleri could not be just simply brought back to life en masse.

True. I’m not sure the Valar ever did anything en masse.