Not sure what the mystery stories are, but looks like each story was published by one publisher before as they are writing the introduction.
Paul's description in the announcement:
'This is a very unique book for us as it marks our first release in the mystery genre, containing six stories by six different authors, along with a new introduction written by the original publisher of these tales. The edition will be available in two states: Lettered and Numbered. Both editions are signed by all contributing authors, as well as the artist.'