It seems to me that, in researching this song, I've seen a lot of sundry verses derived from other songs using this format ("The Murder of F. C. Benwell, etc.), but yes, most other versions are short -- usually no more than five verses.

All those borrowings are responsible for the long list of absurdities in the song. Guiteau wasn't "in his youthful bloom"; he was forty years old! He did have a sister, but she was soon to be institutionalized for insanity. His mother -- who had delusions -- had died in 1848, so she could hardly die in sorrow. And his father was a religious fanatic who probably would have approved of hanging his uncontrollable son.

Insanity was only one line of defense he tried, and it was never going to go anywhere; he met the M'Naughton standard of knowing that murder was wrong. His main line of defense is that he didn't kill Garfield; Garfield's doctors killed Garfield. Which is true, but the doctors wouldn't have been treating Garfield if Guiteau hadn't shot him.

Moreover, although people have argued over the years that Guiteau had schizophrenia, he clearly did not; a schizophrenia diagnosis requires delusions, hallucinations, or disorganized (incoherent) speech, and he had none of these. He was an absurd bore and a thief, and everyone he ever went near despised him. but not schizophrenic.

I could go on, but you can always read the Ballad Index entry on this song, which says all the same stuff.