Old villagers from before 1.14 don't gain any experience when being traded with

I have villagers that had most trades unlocked pre-1.14. When this update came around, (1.14 overall, not just 1.14.4) and the new "leveling" system was introduced, I have had no luck unlocking more trades from villagers. Although they did keep their old trades,  whenever I trade with them, they gain no experience to increase their overall level. (In this case, from Journeyman, to Expert.) And, as such, cannot unlock more complex trades. They have both beds, and workstations.