We do??!?!
Given the current state of DC continuity (or, as we say, "continuity"), I feel like I have no idea. I see constant discussion on this board about whether the most recent version of the founding of the Justice League (The New 52 version) was actually a "founding," or a "refounding" after the League had been around for a while and then - I'm not quite sure - took something of a break. Or, at least, whether it will be treated that way post-Rebirth and post-
Doomsday Clock.
And, if that's so, whether J'onn J'onzz was a founder but not a refounder, and whether Cyborg was a refounder but not a founder. And, of course, Cyborg's status is entangled with what earlier Titans stories would look like.
[Note: In
Justice League #38, out today, Vic says, "I
founded this team, Simon." Well, that's
one data point...]