The first thing to note here is that very nature of such songs easily lends itself to new material being added, so that the big surprise with this song is that many versions utilise a solid core of regular stanzas.
I presume you have the reference to what must surely be the same song mentioned in The Complaynt of Scotland' of about the same period. Some have tried to claim that this actually refers to 'Tamlin' which is highly unlikely.

Looking at the 'Longer thou Livest' stanza where it states 'Synging the foote of many Songes' does this actually mean singing song endings or choruses perhaps? That particular stanza is very often the last stanza for obvious reasons.

>>>>>It's curious that Wager's stanza is so much closer to modern versions<<<<< Not so curious when we see that the song has been continuously in print for four and half centuries and obviously extremely popular in all corners of the English-speaking world. An old version gets printed and becomes very popular again. Several variants running side by side for long periods.