EviaForever
I'm very weird for the CC **** CC series! It will be the Bulgaria's first series with 4 same letters [until today Bulgaria had A AA, B BB, C CC, E EE (trailers in Blagoevgrad) and T TT)
I am glad you are enthusiastic, but... let's not forget CC **** CC was issued besides with Bulgarian flag plates, as it was the third such serie in order for these ones. And Muravei_25Rus spotted a great bingo from it of course ->
https://platesmania.com/bg/nomer14767212 To continue with, A **** AA and C **** CC were oldstyle 1992-1999 period series, so they were the first two ones from the current format. But however, yet you missed to note my hometown province in the list

- as logically in Ruse it was P **** PP, and coincidentally or not as in Silistra it was the third serie in order with flag plates.
When it comes to province series matching their oblast code although, it is in my opinion not that surprising, as I will list them consecutively except the ones you mentioned: EB **** EB (current series for trailers), BH **** BH, CA **** CA, CM **** CM, CH **** CH, TX **** TX (flag plates), BP **** BP, BT **** BT, CB **** CB (EU plates) & PB **** PB + CT **** CT (oldstyle plates from 1992-1999)