I've come across what appears to be a bug. Some loot-table overrides in datapacks/{pack}/data/minecraft/loot_tables/entities are not actually being used. For example, as a simple test, I extracted the default json files out of the 1.15.2.jar file.  The only change performed to the json files extracted was to change the minecraft:rotten_flesh entry [or other default drop] to minecraft:sand. Modifying the zombie.json file yields the desired change, however if I make the same change to husk.json I still get rotten flesh instead of sand.  (I've found that blaze, and drowned, also do not track with overrides, always using the vanilla behaviour, there may be others, I've only tested a handful)