Technically, there’s nothing in Cthulhu that doesn’t let it take place in the mainstream BCyc universe. I’m now of the mind that all BCyc games take place in the same time line, unless the events in them makes it impossible or they branch into an alternate reality: fan disc crossovers being the most obvious.
It’s just some games are more direct in connecting with each other: MDB is directly GSS… Mushi is directly Extra… Gun Katana and the Sayoko-verse reference the Neko Metal band… etc