James McCormick at 2012-06-29 08:39:24:
Pretty sure the Jamie Moss/Josh Schwartz trivia is backwards.
Sheldon Turner wrote the first draft (a couple drafts actually) from a story Bryan Singer pitched. It was set in WW II era. It was called Origins: Magneto (Or Magneto Origins, I forget which). It was concurrently developed at the same time as the Wolverine flick which had a similar title Wolverine Origins which became the Hugh Jackman, Ryan Reynolds flick.
Sheldon Turner's story was almost entirely centered around Magneto. He was the only mutant in the story (save two concoctions at the end) and a brief run-in with a young Charles. The story also had a framing device. It started and ended with old Magneto.
The story wasn't working for anyone (It was pretty bad tbh. Not knocking Turner. It just wasn't an X-Men script) -- so they hired Jamie Moss/Josh Schwartz to have a go at a new take on it. The script they wrote was titled something like X-Men: Year One. This one was set in the Cuban Missile crisis Bay of Pigs era, but had different mutants than they end up using in the final film. This was more similar to what ended up onscreen.
They brought in Matt Vaughn fresh off of Kick-Ass/Stardust. He brought his writing partner Jane Goldman in to do a couple rewrites, which became the script X-Men: First Class.
Because of the number of writers, the script went to automatic arbitration. Because Sheldon Turner had been the first writer (working off a story Singer pitched), they ended up getting a writing credit -- even though the brunt of the story you see onscreen was laid out by Moss and Schwartz.
In subsequent interviews, Sheldon Turner even comments on how ridiculous a decision that was.
I'm 99% positive that's the history of that script.