There are just four stanzas, Phil. Some websites have carelessly combined verses from earlier versions, which were also published. Junk begets junk.
If you look at your 'extra' stanzas, you'll probably recognize them as 'first drafts' of what we know now.
And I completely agree with the others ("get the words right"). There's the Mondegreen effect, plus the situation where somebody's version got popular, but he didn't know the right words.