I agree with a lot of these, but Friday the 13th was clearly retconned between 1 and 2 and should be replaced with Nightmare on Elm Street.
Throughout Nightmare on Elm Street, Freddy is still Freddy and the details they change weren’t forced to make a decent sequel.
Friday the 13th was obviously retconned between 1 and 2. Spoilers for Friday the 13th parts 1 and 2 below.
Tap for spoilers
Jason is only in part 1 right at the very end, of course, and he’s a younger boy, 14 or so, kinda skinny, living at the bottom of Crystal Lake. It’s one of the best jump-scares ever if you’re not expecting it.
They made him a huge, hulking adult in part 2, retconning the major jump scare in part 1.
I think they talk about this in the book Crystal Lake Memories. They had to make him more menacing to make it interesting.
They weren’t wrong, it became the series trademark.