He wrote the string quartet part that backed Paul and his guitar on “Yesterday.”He wrote the string octet part that was the musical basis for the song “Eleanor Rigby.”But he didn’t transcribe the Beatles songs or anything like that.In pop music, creating the sheet music is usually just about the last thing that happens.
But the music was almost always in their heads.George Martin was a excellent arranger. It’s simple-they remembered them.The Beatles would sometimes write the words down.