When I trade with villagers, their trades do not get upgraded. When testing on other villagers outside of my survival world, none of them would get updated, regardless of biome, except for a single farmer in the jungle. The picture below shows a tier one trade for a tundra leather worker being used to the max, and despite doing this and waiting for some time, the villager would not receive regen, have his badge upgraded, or have it's trade upgrade.