Absolutely! To my understanding, they didn't know much music theory at all. It was all intuitive and through experimenting. They didn't even write their music down in musical notation. "Couldn't read music" I think? At least early on. One clue of how they did it is a McCartney quote I heard recently, something like, "One of us would learn a new chord and we'd teach it to the others and write a song around it."