The reasons we've got all these folk variants is because people mostly sang and passed them on from memory rather than relying on the broadsheets they might have picked up.

And more often than not the variants are a lot better than the originals. That's more or less what that term "the folk process" adds up to. And long may it continue.

Most singarounds I've been in over the years have been overwhelmingly made up of people singing from memory. No rules about it, just generally the custom.