Slitherine

I'm sure the answer must be simple but maths is not my strong point so can anybody tell me why my two yellow-arrowed cities aren't generating any prestige points for me?
I'm the Russians in a 1941 random battle and the jerries are walking all over me, I occupy only those two cities, the major one should be generating 40 pp's and the minor one should be generating 20 pp's, plus I should be getting 70pp's per turn (Colonel difficulty level) but my total pp's at the top of screen have been stuck on '91' for the past few turns!

On second thoughts I think I vaguely remember hearing somewhere a while back that if you set Turn Limit to "Off", the game will continue forever past its default end turn like this battle did, but you won't get any more incoming pp's during that extra time.
I'll run some searches to try to confirm it.