Zeta (Montenegro) was part of Serbian Despotate in 1444, not a vassal state.
Even Srebrenica (Podrinje) was changing rulers every few years 1411-1449, and at one point around 1444 they produced coins with Serbian despot Djuradj Brankovic on one side, and a Bosnian ban on the other side, this province should have a Serbian core as Thessaly has Venetian core.

About Montenegro:
https://en.wikipedia.org/wiki/Zeta_under_the_Crnojevi%C4%87i


Bosnia:
1) "According to Czech historian Konstantin Josef Jireček, from 1411 to 1463, Srebrenica switched hands several times, being Hungarian one time, Serbian five times, Bosnian four times, and Ottoman three times.[9] The mines of Bosnian Podrinje and Usora were part of the Serbian Despotate prior to the Ottoman conquest."

2) https://en.wikipedia.org/wiki/Serbian_Despotate
"In 1411 King Sigismund of Hungary rewarded Stefan's loyalty with a gift of Srebrenica and its surroundings"
"Serbia was fully restored by the Peace of Szeged on August 15, 1444. Its borders were the same as before 1437, with the exception of the southern part of Zeta, which remained under Venice, and fort Golubac, which was returned to Serbia even though it was lost much earlier, in 1427.
King Tomaš of Bosnia started another war with Despot Đurađ in 1446 and managed to take Srebrenica. However, in September 1448, the Bosnians were defeated by a Serbian army led by Thomas Kantakouzenos, who reconquered Srebrenica and also took Višegrad.[13] "

I see, thanks for this. I shall implement above changes in 1.2 update.