Someone asked why the first verse has AAB lyrics. My understanding is that it's because so many people have been deriving the song ultimately from a particular recording by Jess Morris, and Morris learned the song from a black guy who apparently used AAB lyrics, and a "mixed approach," using stanzas with different rhyme schemes in the same song, such as AAB stanzas with AB stanzas, or AAB stanzas with AAAB stanzas, was downright ordinary among folk musicians born before about 1900. It was the people who made the books who would often artificially "straighten" that "mixed approach" out.