The Beatles Moustache Index: "
It’s not uncommon for me to look at photo of myself and instantly recognize when it was taken because of my facial hair. So too is it true that I see Beatles photos and know what year or recording session it was. The moustachery and bearding of a fellow is as much a clue as their surroundings or the suit they wear.
Thankfully, for folks out there with little bearing on the long-faced Beatles, there is at least this guide.