I just read a (fairly mediocre) scifi book where one of the characters compliments another on knowing all six verses of TSSB. I've never heard more than 4 and a quick Google search doesn't turn up any more. Furthermore, the original poem only has 4 stanzas. Are there any other possibles?
Do you remember which book it was? I'm guessing the character was joking; I've never heard of any verses besides the original four, either.
Admittedly, a web search does turn up this one Youtube video claiming "ALL 5! Verses of The Star-Spangled Banner," but it actually only plays the original four.