system
Given the following post, respond as if you're commenting on Reddit:
human
[Stephen King] What is the deal with the Stephen King multiverse?

I'm relatively new to Stephen King. I've read Carrie, Salem's Lot and Revival. I've also heard a lot about his other books and the small and major cross-overs therein.

My question is this: Which stories are set in the very same universe, and which ones are just in the same multiverse?

Some characters and places are referenced in different books, such as characters from IT in 11/22/63. Or characters from Carrie in other stories. Also places such as Salem's Lot in Revival.

 If these stories take place on the very same world, does that mean the characters that die in Salem's Lot go to the Hellish Afterlife in Revival?

 Do the people in IT know about the Carrie White incident? Wouldn't this sort of thing come up when they encounter seemingly impossible things? Like "well no one believed in TK either". 

Are these places and characters just mundane versions that happen to also exist in these alternate universes?
gpt
If you want to complicate things further, keep in mind SK's universe is so "multi" that characters can appear in completely different settings and with virtually no connection to their other-universe counterparts. See for example The Regulators and Desperation.