I have a theory about Astarion's magistrate background...
I've always wondered how Astarion can still remember his magistrate professionalism and can even offer it as a skill to Wyll to find any loophole in Mizora's deal in the origin run despite the fact this guy doesn't even remember his eye color. After reading "Astarion's book of hungers" by WotC I got an idea.
So in the book Cazador is a vampire infernalist and in his circle there's one type of devils called "harvester devil" who specializes in making contracts with people to trade for their souls. But they are often too quick to make deals and they may leave loopholes in their contracts. The key to dealing with these devils are finding loopholes in their contracts. Astarion even has a comment about them: "Unfortunately, finding these dandyish devils' contractual loopholes is not nearly as much fun as I had hoped." It implies Astarion has dealt with them and tried to find loopholes in their contracts quite often. That's why Astarion still remembers his magistrate background, because he had to recall and use the skills.
It may even fit as an explanation why Cazador chose him. There could be multiple factors in it but one of them could be that Cazador knew he had to deal with these devils and he wanted to get himself a spawn who seemed to be especially good at it. Astarion might be the kind of magistrate who got the cunning skill in finding and utilizing loopholes in rules to his benefit.
However, there's also one loophole in this theory: Astarion doesn't know infernal. He should be able to read infernal if he's often played finding loopholes in the devils' contracts. Instead, he knows Abyssal according to his official character sheet. That's really confusing but I can think of a reason. It's probably because Cazador prohibited him from learning infernal to stop him learning the meaning of the scar on his back by any chance.
Furthermore, it can also be the reason why Astarion was eager to make a deal with Raphael and why he could immediately figure out how to finish the ritual to make himself ascend, because the ritual is basically a contract with Mephistopheles.
Anyways, I know there're a lot of loopholes in the story and WotC's book might actually make it even more messy, but these are just my headcanons and my efforts to connect the dots.




















