This is really interesting - must have been a lot of work! I'd wondered about it myself. One other bit of canon I don't know if you took into account - what's the episode where Fraser's reading Bob's diaries, and one from 1969 has him talking about Fraser being 'seven years old and already more a man than I'll ever be'? If we get a date for that, Fraser's birthday must be after it, because I'm pretty sure he was born in 1961, so he'd be turning eight in 1969.