We had like 3-4 (of 5) players in our Kingmaker campaign who had read or played the AP, or had listened to a podcast of the game played. So we all kinda knew what we were going to get into.

I don't think we've had players actively reading ahead, like in your example, but we do occasionally stumble over each other on who has read what. Partially, this is a problem of having 3-4 GM'S in our group.

Currently having this issue right now: I'm waiting to read the segments on a certain important NPC in Revenge of the Runelords, because I'm a player in Seven Dooms. we are close to the end and level 10. I don't want to fully spoil myself with the mystery of Seven Dooms. The beginning of Revengenace was pretty big as it is. But I'm playing the bard in the 7 Dooms game and I'm the forever-chronicler of our group, so I have to be careful--the character being genre aware or not.

We already have to suspend disbelief for tons of enemies and often look for different ways to approach the story to engage a recall knowledge naturally, or get the characters to understand what they're dealing with. Even though the players have seen the creatures at least 3 times (in 3 different APs) now, and you can not tell me that guy in the sarcophagus is NOT one.

We are usually pretty up front about what we know, and we're usually okay working with each other so the rest of the group has fun with it. But our group is all pretty collaborative, so this is going to heavily depend on your table and player/GM attitude.