This came in recently:
Lovecraft, H. P. (edited by S. T. Joshi). H. P. Lovecraft’s Collected Fiction: A Variorum Edition, a three volume set consisting of Volume 1: 1905—1925, Volume 2: 1926—1930, and Volume 3: 1931—1936. Hippocampus Press, 2015. First edition hardbacks, one of only 750 sets, all Fine copies in Fine dust jackets and shrinkwrap, new and unread. “For the first time, students and scholars of Lovecraft can see at a glance all the textual variants in all relevant appearances of a story—manuscript, first publication in magazines, and first book publications. The result is an illuminating record of the textual history of the tales, along with how Lovecraft significantly revised his stories after initial publication. Along the way, Joshi has made small but significant revisions to his earlier corrected texts. He has determined, for example, that Lovecraft slightly revised some stories when a reprint of them was scheduled in Weird Tales, and he has altered some readings in light of a better understanding of Lovecraft’s customary linguistic usages.” So not only do these three volumes represent the complete and super-duper definitive edition of Lovecraft’s work, hardcore Lovecraft fans can see how both Lovecraft and others revised his work over the years.
Update: They later published, and I obtained, a fourth volume.
I have sets of all four volumes for sale through Lame Excuse Books.