If you add a mod after OpenLoader, any resources that override eachother (in my case, loot tables, but not tags) will have lower precedence than those of that mod.

In my case, in order:

• Added OpenLoader
• Added Towers of the Wild
• Added a loot table to OpenLoader that overrides a Towers of the Wild loot table
• The loot table is properly present in a singleplayer world created after the fact
• Loading up my server which didn't have it previously causes the openloader datapack to be pushed lower than the newly added mod's, as such: