slave get promoted to tribesman - I would expect freeman

[spotlight2001]

nation: sciria (vandal)
migratory tribe

plan: becoming a monarchy
I have re-located tribesman/slaves to my few cities
plan:
tribesman demote to slaves / promote to freeman
slaves promote to freeman

But I have several examples where a slave promotes to tribeman, even with very low desired tribesman ratio.
Why doesnt the slave promote to a freeman which has a much higher desired ratio?

slave is neither in culture group, nor religion

 

[Napoleon1971]

nation: sciria (vandal)
migratory tribe

View attachment 752354

plan: becoming a monarchy
I have re-located tribesman/slaves to my few cities
plan:
tribesman demote to slaves / promote to freeman
slaves promote to freeman

But I have several examples where a slave promotes to tribeman, even with very low desired tribesman ratio.
Why doesnt the slave promote to a freeman which has a much higher desired ratio?

slave is neither in culture group, nor religion

There is a decent amount of randomness on what gets promoted. But, you're a gap of 6% tribesman (wants 6 has 0) and only 5% gap on freeman (wants 25, has 20). I didn't write the code and haven't tried to reverse engineer it. But, I'd think if it decides to promote a slave, you're slightly more likely to get a tribesman since the larger gap (if I was writing it'd be 6/11 once deciding on a slave being promoted).

Perhaps someone knows the actual formula.

 

[Herennius]

I'm not even sure if a Tribe's Slaves and Freemen can still directly pro-/demote into each other since the rules about Tribesmen were changed (in older versions the iron rules was that no pop would ever become a Tribesman, but at some point that was changed for Tribes). I understand the wiki that way that in a Tribe the Tribesmen are in a "middle" position between Slaves and Freemen, but I concede that the wiki text isn't totally clear here (very last paragraph deals with Promotion/Demotion):

Population - Imperator Wiki

imperator.paradoxwikis.com