Hey Rev, There are two different books "De Shootin'est Gent'man", there is the Derrydale and various reprints from 1934 and there is another book with the same title published by Nelson in 1961 which other than the title story is entirely different and has 19 other stories or articles that I believe are not available elsewher in book form.
Also there is Nash's last book "Once Upon A Time" which was published after his death of also un published stories.
Thanks, I enjoy your work.
Lawrence