That's not exactly true regarding the region of purchase. I've bought a model intended for US market, but I use it with European carrier SIM and I get updates. But I had troubles with getting updates with NZ carrier SIM. I think that happened just because NZ carriers approve updates only for models being sold in NZ, so other models just gated off.
Things are even more complicated with models intended for Mainland China. HMD uses different update servers which are maintained by FIH Mobile, because Google is blocked in Mainland China. And I reckon even less carriers approve updates for Chinese models. Though I know that people in Russia get OTA updates on TA-1000 (China), TA-1003(HongKong/Taiwan) models
I got august security update today in india TA-1021