The region wealth is the base for taxes. So, if the region wealth is 1000 and your effective tax rate is 35% you get 350 from that region in taxes. It's the same before and after the patch.
Post patch: if the wealth of the region is increasing (buildings, roads, trade, humanitarian techs, etc.) you will see your tax intake go up as long as you're not expanding too fast effectively lowering the tax rate.
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