Was it really just a shock to me that the characters BG-1 & 2 appear in BG-3?
After the events of the second part, many years have passed on Faerun. As far as I understand, more than a hundred years. Minsk in BG-3 should look something like Arnold Schwarzenegger today. It would be sad and unpleasant.
Nostalgia? Great. Here's a Sarevok for you. Enough
I will go even further, by lore, Jaheira is dead. She died in book three for the Baldur's Gate Novels.
