I converted my world from 1.13.2 version to 1.14 version. With the villagers it only converted the unique types (clercs, cartographers, tool smiths) but did not convert the farmer types (Farmer, Fisherman, Fletcher). The farmer types still have their 1.13.2 and older brown robe look to them, but do not trade with the player and works just like the NitWitz.

I have seen zombie farmers spawn at night with the new look (havent had the chance to convert), and when I start a new world in 1.14 version the farmer types work just fine.