Detecting Marian Legion Reform and Imperial Legion Reform

[kronenblatt]

What is the easiest script-wise way to check whether Marian Legion Reform and Imperial Legion Reform, respectively, has taken place? (I'll be using it in a mod.)

EDIT: NM, found it myself: it seems to be Evt_Rome_Marian_Tracker and Evt_Rome_ImperialLegion_Tracker, respectively.

Do they take place for Rome, given that certain triggers are met, or upon certain years?

EDIT: It seems Imperial Legion Reform requires Marian Legion Reform, but that they are more or less random, with probabilities to occur increasing as time goes by. Correct?