Only the flavor text refers to this for Deltascape v3 and v4. However Omega says different:
https://i.imgur.com/xJz8OIx.jpg
And Nero also says this:
https://i.imgur.com/wCXRgPB.jpg
Note "recreated", these are all defeated bosses from other dimensions.
For the sake of continuity, the only games that makes sense is FF8 or FFX, and since FFX actually has a different backstory for Omega, FF8's the most obvious one. That said, they could do both. Nobody said they had to stop at 12.
Omega specifically says 89. So if you do the math for ranked match, either there are 8, 4 or 2 ladders with one remainder. Delta(Δ) is "4", Sigma(Σ) is "200".
If you want to get into continuity fumbling, FF7 FF8 and FFX 's main protagonists all got put into kingdom hearts. So FF7 is probably overplayed at this point.
It was added to FF6's GBA version, so that's not quite right.
And if we're going to nitpick the difference between Omega and Omega Weapon.
Revised versions of FF1 and FF4 have Omega. Omega appears in FF5, FF11, FF12 and FF13-2, and FF15
Revised versions of FF6 have Omega Weapon, Omega Weapon appears in FF X, FFX-2, FF7(Dirge or Cerebus)
