so different, yet so clearly the same

Just a thought, but it's obvious to spot the differences between two disparate versions of the 'same song', but what about the versions that immediately preceded it? or yet came after? What about the next time the song was sung by the same singer? I've got examples of Davie Stewart doing this, but a more immediate example is the two versions of Green Wood Side sung by Mrs Pearl Brewer on the Max Hunter Archive. The creative process of singing means they're both very different, or is it the random factors of memory? Either way, whilst both versions are complete & wondrous in and of themselves, they are, in another sense, only part of a wider condition of change and adaptation as the songs live (and are lived with) before being passed on.