Rule 82: Temporal Clauses 

Yeah, sometimes it's not as clear, especially with postquam. Still, the perfect is standard, and you can think of occasional use of the pluperfect as a way to enforce an entirely completed action: postquam bis consul fuerat, multos libros scripsit, after he had been consul twice (and he's definitely done with that), he wrote many books. As opposed to, postquam ad urbem pervenit, multos cives plaudentes invenit, after he reached the city, he found many citizens applauding. In the latter case, we have two actions that could conceivably be put into two separate sentences by removing the postquam. But you can't do that with the first sentence about being consul. And so that is where the distinction occurs between the perfect and the pluperfect, at least for our purposes. Will you find the pluperfect used in situations where the perfect seems to be perfectly fine, of course! Because language is messy and no one actually follows all of the rules.

EĀMUS!!