Expected behavior:

After curing a zombie villager, say, a librarian, a 25 emerald discount is applied to all of that villager's enchanted book trades. This discount never decreases.

Actual behavior:

After 1 real life day, the 25 emerald discount has been reduced to 20 emeralds. In 1.14.3, this would have happened after 1 minecraft day and continued to decrease in increments of 5 after each successive minecraft day. I expect that that time has been substantially increased in 1.14.4 to something like 10-15 minecraft days, but not removed.