It would seem that, as a forbidden work, The King In Yellow has attracted those who would make their own versions - possibly to profit from the gullible, possibly due to madness. This would explain why details of the play seem to vary from source to source and its age tends to vary. Of course, it is possible there never was a genuine play and that all copies are the work of madmen driven by an urban legend - not that that necessarily makes such copies any the less dangerous...