That's very interesting. I think I've mostly seen that term used in connection with the Munsey magazines, which also used the term "different stories" for stefnal material sometimes. A while back I meant to write about George Allan England's introduction to his Darkness and Dawn trilogy (originally published in Munsey magazines starting in 1911), where he used the term "pseudoscientific stories" to describe the genre of these novels. I can't remember for sure at the moment, but I think he wrote that intro for a book edition in the early- to mid-20s. I hadn't realized that the usage had spread to library catalogs. Considering the amount of nonsense or hand-waving that gets passed off as science in SF, it's a term that immediately appealed to me.