How many times have you heard an old favorite played by it's original artist and he seems to have changed a line from one verse to another or changed the order of the verses. Or added a chord or note different from the recorded version. Or played a verse twice.
We always chalk it up to him intentionally making changes. I think it's mostly unintentional.
If you listen to Bob Dylan live, you might find him using the lyrics from one song with the chord progression and melody from another. I always wondered if that was intentional.