Minecraft 1.11.2, Minecraft 17w06a, Minecraft 1.12 Pre-Release 6, Minecraft 1.12 Pre-Release 7, Minecraft 1.12.2, Minecraft 17w45b, Minecraft 17w46a, Minecraft 1.13.1, Minecraft 1.13.2, Minecraft 18w43c, Minecraft 18w47b, Minecraft 18w48a, Minecraft 18w48b, Minecraft 18w49a
Client-side an incorrect villager career name might be displayed when the CustomNameVisible tag of a villager is set to true but no CustomName is set.
In the attached screenshot 2017-11-22_12.45.22.png you see a "Shepherd" (GUI title and trades) with the name "Fletcher".
Use the following command and compare the shown name with the trades and the name in the GUI
Note: This might require multiple tries since the client could randomly pick the correct Career.
Based on 1.11.2 decompiled using MCP 9.35 rc1
The Career value of a villager is not send to the client, therefor it randomizes it. Additionally the client should very likely not call the method net.minecraft.entity.passive.EntityVillager.populateBuyingList().