And Wikipedia: "Marvel numbered stories through 1985 up to number 20, but released many other stories in the same format that are considered unnumbered parts of the series according to the Official Overstreet Comic Book Price Guide. Overstreet continued counting beyond the original "official" numbering, following a Marvel-published list of graphic novels. When the list stopped being published, Overstreet stopped trying to number the issues, halting at issue 38, although they list 29 more issues published from 1983 through 1991, although the list is known not to include every graphic novel from this period."
I am seeing this also. Not every graphic novel is in the list I have of marvel graphic novels from this period.