Updates on Susan and Deb's research are posted on The Twain Shall Meet
facebook page as new discoveries and links are found.  To my knowledge, the
first DNA envelope offered for testing failed to find usable DNA due to the
age of the sample.  Susan's matches to known descendants who have provided
DNA to a national database continues to rise.
There are also many other letters from Nina's estate that were recently
found to be at the Mark Twain Papers that were unknown to Susan and Deb at
the time their book was produced.  I understand these are being transcribed
and made available. One other scholar who has researched Nina's life in
depth has also shared additional material.  While Susan may never attain
that 100% certainty mark, the percentages for her being Nina's daughter are
extremely close to that.

I do expect there will be an updated second edition of their book at some
point in time. I agree with Hal that this story is one that would be of
prime interest for a venue such as the History Channel.

Barb