Glad you asked that.  It is a good and fair question.

Almost all biographies before WWII, let alone WWI, inevitably are "iced out'
as major biographies, no matter who the subject is.  New materials, letters,
journals, unpublished writings, archives, and so on, provide much more
information as time goes on.  Henderson had no access to probably 95% of the
vast wealth of materials that the Bancroft Library at Berkeley has available
to scholars.

Also, methods of literary and historical study, not to mention just our
contemporary ways of looking at life and culture, are drastically different
from 1910.

Nevertheless, we can learn a lot from older biographies.  As a matter of
fact, I learned a lot from Henderson's book and was delighted to discover
it.  To give one glaring example that is near and dear to my own heart,
among other things, Henderson's volume has a very good overview of Twain's
views of Christianity and the religious life that many biographers have
either overlooked or misread (IMHO).

In addition, these older bios are often rich in anecdote and good
old-fashioned story-telling.  An excellent example of this are 19th-century
biographies of Lincoln, which are still great reading.  Importantly, they
also vary wildly from author to author--which is another point about getting
iced out.  Older bios tend to be much more hagiographic.  Not always (see
Van Wyck Brooks).

Henderson tells some good stories.  He interviewed and corresponded with
many living people who knew Mark Twain personally.  Not to mention the plain
and simple fact that he actually talked to Twain himself!  To the best of my
knowledge, no member of this Twain-LIST can say that!

Dr. Harold K. Bush, Jr., Associate Professor
Saint Louis University