While on the topic of copyright, if I may ask, what makes Twain's
works/notebooks/letters/misc published AFTER 1923 subject to
copyright?  While I have a general sense of the answer I am still
confused how they have a copyright beyond the standard 70 years after
the author's death.

As for his works after 1923, what remains of their copyright?  Is it
specific to each document?  I always had a sense that copyright began
with the creation of a work not its date of publication.

Alex Effgen
Boston University