So I've decided to write my own loot tables using the blank ones already present, in order to make GoG compatible with mods like Tiny Mob Farms I have in my modpack. 99% of them work nicely, but I've run into a small handful of issues:

The alternate form of the witch (orange hair) uses the vanilla witch loot table instead of the mod's one.
Armored orc uses the orc_ranged loot table instead of orc_melee.
Ranged orc uses minecraft/empty loot table instead of using_orc ranged.
Both minotaurus variants (ranged and melee) use the same minotaurus loot table.
Mimic is a massive headache... It doesn't use the mimic loot table at all, and instead keeps switching its loot table between vanilla mobs, making it impossible to get its unique loot, or any of it for that matter.

Any idea on how to fix that?