I noticed that custom item tags created through a datapack remain even in worlds not using the pack until the game is closed and reopened. For example, in one world I use a datapack that creates a tag for all potions. 

However, when I open a different world without the pack, it remains.

This seems to stay until the game is closed and relaunched. It's not just visual either. It remains functional. I can search the inventory using this tag and run the command to clear all of someone's potions.