Part of my mod doesn't work when exported and played in regular MC

Part of my mod registers/tags a couple items and blocks in the OreDictionary for compatibility with a different mod.

When I test my mod with the other mod inside MCreator as usual, that mod recognizes my mod's tagged items and blocks like it should. However, when I export/compile my mod and run it with the other mod in Minecraft (not MCreator), the other mod doesn't recognize my mod's items and blocks anymore...

I spent a while trying to figure this out, but I can't find anything. It should work. It works in MCreator, but doesn't work once I export and play it.

If anyone has any idea what might be up, I'd appreciate the help!