So now, as I see it, they have enough material for three more trades:

Vol.3 would contain America vs. the Justice Society #1-4, from 1985 (138 pages plus 4 covers), and the Last Days of the Justice Socity Special from 1986 (64 pages plus cover)

Vol. 4 would be the 8-issue Justice Society miniseries from 1991 (176 story pages plus 8 covers).

Vol.5 would be the 10-issue continuing series from 1992 that was drawn by Mike Parobeck (221 story pages plus 10 covers)

Let's hope they're all planned.
Who am us, anyway?
--The Firesign Theater