First problem: When do Remus' friends figure out he's a werewolf?
"My three friends could hardly fail to notice that I disappeared once a month. I made up all sorts of stories. I told them my mother was ill, that I had to go home to see her... I was terrified they would desert me the moment they found out what I was. But of course, they, like you, Hermione, worked out the truth... And they didn't desert me at all. Instead, they did something for me that would make my transformations not only bearable, but the best times of my life. They became Animagi. ... It took them the best part of three years to work out how to do it. ... Finally, in our fifth year, they managed it."
Fifth year is 1975-1976, minus three is 1972-1973, second year. But the HP Lexicon lists it as "late 1971." I'm not used to second-guessing the Lexicon, this is hurting my mind.
You know what? I'm just going to have to respectfully disagree. They list the Marauders' NEWTS as c 1977 [deduced from birth years], which was Spring 1960 for James. That means they started Hogwarts in September 1971 and sat their NEWTs in June 1978. I'll just add a year to HPL's date whenever I need to and move on.
Actually, that lets me resolve the date of Sirius' tricking Severus. I have no idea why HPL is listing it as September, Remus only described it as "one night" (PA18) and Lily as "the other night" (DH33). But sure, why not. Early in year 6 works out for what I want.
Well, that's one thing taken care of!
EDIT: This isn't taken care of at all! Snape's Worst Memory is June of 1976, end of fifth year, no way to get around it. He and Lily were friends but fighting around the time Sirius tricked him, which I have later in 76, at the beginning of Sixth year. THIS DOESN'T WORK AT ALL. can I move it to late 1975? They'd be fighting for a whole year then. Not tenable. Or early 1976, that would give the Marauders time to become Animagi and for Severus to get suspicious of them. okay. Everything from canon goes down fifth year, then.
I've got some surprises for later, don't worry.