I've been curious about this game for a while now. Apparently, the original PC-98 version of Corpse Party was to receive a sequel, made in the same version of RPG Maker, but it was cancelled. The Corpse Party wiki has some info about it, describing a reported demo of the game. There's also a NicoNico video that claims to have soundtracks from the abandoned project. (https://www.nicovideo.jp/watch/sm10895078) Elements from the game, such as the protagonist, Satsuki, were brought into later installments of the series, and there have been small references to the cancelled project here and there. Which, I suppose, lends credence to the game having existed at some point. What I'm really curious about is how all this detailed information was found and wether or not the demo still exists, or ever existed.