In 1.14, with the introduction of the Village and Pillage update, trading was revamped significantly, discontinuing many villagers because of their pre-1.14 trades that were different to post-1.14 trades. This can be combined with pre-1.8 villagers or 1.14+ villagers.
The trades are unlocked by tier and so even fully available trades in 1.14+ can be discontinued by being in the incorrect order or by being before another discontinued trade.
The items of the trade are available but only in different counts than the trades available 1.14+
Certain Quantities
The items of the trade are available and some of the quantities are available but other quantities are not
Available
The trade, including its quantities, are fully obtainable
Other
Special cases, check reference for more information
Professions
Farmer
The farmer profession includes four careers, farmer, fisherman, shepherd, and fletcher. Updating a pre-1.8 farmer into this version range will assign it one of these careers randomly unless the GUI is not opened, in which case the lack of a career is not updated.
↑The quantity available in 1.14 - Present is 20 Wheat for 1 Emerald
↑Upon updating this will become a regular pumpkin instead of a carved pumpkin unless updated to 17w47a to 1.13-pre1 (1.13 snapshots), in which case it'll become a carved pumpkin trade
↑The quantity available in 1.14 - Present is 2 Emeralds for 1 Bow
↑Certain quantities of this trade are available in 1.14 - Present, however the first and second buy slots are reversed
Librarian
The librarian profession includes two careers, librarian and cartographer. The cartographer career was added in 16w39a (1.11 snapshot), unlike the other careers, which were all added in 14w02a (1.8 snapshot). Updating a pre-1.8 librarian into this version range will assign it one of these careers randomly unless the GUI is not opened, in which case the lack of a career is not updated.
↑The quantity available in 1.14 - Present is 24 Paper for 1 Emerald
↑The quantity available in 1.14 - Present is 7 Eemralds for 1 Empty Map
↑Certain quantities of this trade are available in 1.14 - Present, however the first and second buy slots are reversed
↑This trade is available in 1.14 - Present in different quantities, however the first and second buy slots are reversed
Priest
The priest profession includes only one career, which is the cleric. Updating a pre-1.8 priest into this version range will assign it the cleric career unless the GUI is not opened, in which case the lack of a career is not updated.
The blacksmith profession includes three careers, armorer, weaponsmith, and toolsmith. Updating a pre-1.8 blacksmith into this version range will assign it one of these careers randomly unless the GUI is not opened, in which case the lack of a career is not updated.
↑ 1.01.11.2A random enchantment of level 5-19 is assigned
↑The quantities available in 1.14 - Present are 7-21 Emeralds for 1 Enchanted Iron Shovel
Butcher
The butcher profession includes two careers, butcher and leatherworker. Updating a pre-1.8 butcher into this version range will assign it one of these careers randomly unless the GUI is not opened, in which case the lack of a career is not updated.
Villagers can be used to overstack items in buy slots from 19w13b (1.14 snapshot) to 1.14.1 though. This allows a librarian with a written book trade to overstack it, this trade is also possible with pre-1.8 villagers.
Uncraftable Items Crafting Statistic
Due to a glitch,[1] trades are counted as crafting that item. Because of this, after a 1.10 snapshot (see bug report)[test], the villager can be used to get crafting statistics for uncraftable items. These trades give discontinued crafting statistics: apple, bottle o' enchanting, enchanting book, ender pearl, flint, filled map (from explorer map), name tag, and saddle. All of these trades are also obtainable in 1.14+ except for the flint.
Max Uses Over Normal Limit
Prior to 1.14, the MaxUses for each trade would increase by 2-12 each time offers are refreshed. When updating to 1.14, the MaxUses remain the same, allowing you to create villagers that are able to trade hundreds of items before needing to restock.