Yep. Don't forget region = <region name> in their country files, that's what makes them regional countries.
I did created two regions just to test it, and as I mimicked other regions I did not forget that
OK, it's flag time:
Maurya Empire (buddhist wheel, I know in the beginning this wasn't a symbol...)

Anuradhapura (flag from wikipedia, coloured by me)

Chera (copied details from a coin)

Pandya (copied details from a coin)

Chola (copied details from a coin)

Kalinga (the name of the country in the script)

Minyue (copied details from a dish or something like that)

The following ones are obvious: the name of the country in the script
Chu

Han (the warring state, not the big dynasty later)

Qi

Qin

Wei

Yan

Zhao

Van Lang

The colours were my addition. Criticism needed.