Out of extensive testing, I can tell you that in series ONE, with limited nations statement, you get per terrain only those aircrafts for nation listed. Provided that EXPOrt is marked as FALSe per airplane. I bet your sukois were marked as export true.
I don't know in series TWO, but I guess that all what userlist function (not available inseries one) does is limit the exportavailability for the antions (and the skins) listed in userlist. So in a terrain you have only france and germany and the system will pick according also to enemy and friendly statments, only planes from natiosn france and germany, or planes with export = true. In series TWO, also, the userlist.ini will limit the export. IE a terrani with nation, say argentina, will pick a mirage with nation france and export = true.
But won't pick a Rafale maybe with export = false, or won't pick another Mirage version whose userlist does not contain argentina.
EDIT: just tested on series one, with a nation named Target Drones , the limited nations statements, (and obviously an enemy airport) I have only QF-104, QF-4 QF-100 (whose nation is now target drones) showing above the terrain.