According to a reference note in _Mark Twain's Letters to His Publishers_,
(p. 236) Fred Hall reported back to Twain in a letter dated 28 October 1887
that Belford & Clarke publishers had granted permission for their work to be
included in Twain's _Library of Humor_ which was published in 1888.

Any theories as to why would Twain apparently negotiate or allow his
agents to negotiate for publication rights for any work that was owned by
one of his most notorious enemies -- the former Canadian "pirate" Belford?