I have been in full control of the three towns that trigger the AG South split for two turns. I had the same thought that the split might happen the turn after capture but it did not.
I plan to play one more turn on the off chance the AI wasn't set set up to split as early as June.
If the split does ...

I purchased the game when it was on sale from Matrix a year ago so I assume it is the latest version.
This problem is more than just a "German player complaint". Without the extra HQ it is impossible to push into the Caucasus which ends the game for me. After hundreds of hours invested this is ...

I am playing the campaign game as the Germans against the AI. On turn 54 I captured the towns of Azov,Manych and Bataysk which should have caused AG South to convert to AGs A and B. This did not happen.
I thought perhaps the change would take place at the beginning of the next turn but again it did ...