DC Special 17 (Summer 1975) is devoted to Green Lantern reprints, with a great Mike Grell cover. At this time, Green Lantern had lost his book and was appearing as a back-up series in the Flash. This issue reprints three tales, including the first time Green Lantern met the Guardians of the Universe, and the debuts of the Weaponers of Qward and Myrwhydden.
Green Lantern got a second reprint issue with DC Special 20 (Feb/March 76), once again with a Grell cover. This collection includes the story in which Tam Kalmaku learns that Hal Jordan in Green Lantern, the first time Hal went to the year 5700 AD and became Solar Director Pol Manning, and the debut of Katma Tui.
I am sure these two issues were looked at, sales wise, as tryouts for giving Hal his own book back. Sure enough, a few months after this, Green Lantern was revived, with Mike Grell on the art.