My headcanon is that Sam told Dean vaguely what happened in Mystery Spot, and Dean told Sam vaguely what happened in 2014, but a lot of emotions and significant details were left out. Probably they'd play it to each other as a pain in the ass than a really painful thing. And you're right about the Carver Edlund books, though I doubt Dean would want to touch those. And now I want fic where Dean reads Mystery Spot and thinks it's hilarious and Sam is like >( NOT FUNNY DEAN. Though wait, didn't Dean say something about his deaths in Mystery Spot in Changing Channels though?