Leader Maximum Negative Traits

[Brodosaurus]

I have -3 to maximum negative traits and my leaders still get them, so it's at least 4.

It is randomized, the most common number is 3.
But you can get unlucky leaders who can get up to 4 of them, so even with -3 you will have sporadically 1 negative trait.

 

[Brodosaurus]

Is it a MTTH roll that WILL eventually come or is it a check against a value once to see if we get it.
I'm asking because my lithoid necrophage leaders all have precisely 1 negative trait at -3 maximum. Ages between 100 and 180.

If it is a simple mtth, doesn't that mean that long lived leaders will eventually fill up all their negative trait slots?

Hm, it looks like some weird rolls. You can type debugtooltip in console command and see how big the potential negative trait variable is - it should be 4, if you have -3 negative traits on the empire and still got 1 negative on this leader.

Forgot to answer the question, so here goes the edit!
Tbh I don't remember how often the roll is made, but it is a recurring roll, so yes - eventually, the long living species will fill all their negative traits potential. But they should not go over it.
For example, if you have a leader with 2 negative potential - he can get 1, and then for example die from old age before getting the 2nd one. But would you increase his leader lifespan, he will survive longer, so there is higher chance for him to get this 2nd negative trait.