81 stories by Benson are contained in 5 volumes edited by Jack Adrian. --from manual count of database publication records (which presumably lack some contents by Adrian), presuming no duplicates, as of 2018-02-24
See also the contemporary collections Spook Stories (1928) and More Spook Stories (1934), which contain 25 stories. --from manual count, as above
Concerning Hutchinson's Magazine, "the company's prestige title ... of special significance was the long series of 28 Spook Stories by E F Benson (April 1922-August 1929)."
--SFE: Encyclopedia of Fantasy (1997), "Hutchinson's Magazines"