When trading with the new villagers I've unlocked specific trades with the, Such as a sharpness V book or a mending one. I name tagged those villagers so I could quickly find them again. I went to purchase those books and discovered that they had been replaced with a bookshelf and a Respiration II book. I checked some of my other villagers and discovered that their trades had also been replaced. Villagers should keep the trades that they have when the player has traded with them. They did not loose their trade by unlinking with the Lectern that they were linked too, I have them trapped in the same chunk with the Lecterns.