I'm a songwriter and I have co-written songs. I always make sure I credit whomever was writing with me or had a hand in it. I've seen so many take other people's songs (I know I 'm old school and this is the era of song sampling everywhere). It's just a credit and Dylan has enough songs out there to not need it, but. I've seen some heartbroken writers out there who had their work taken and not an acknowledgement to be found. It's hurtful for a writer. And shameful for the thief.