during the first half of their career, until circa 1965, John and Paul wrote and composed together
many songs fomr this era are "50/50" paul and John, for exemple each writin a verse, or one for the chorus, the other one for the verses, etc...
indeed, in the second half (65-70) they did compose and write alone
the french site "yeelow-sub.net" tried to summarize which percent was written by each Beatle in each song