Quests that belong to arathi highlands are shown in the harbor of the horde as available.
They are also shown when the arathi highlands belong to the alliance.
Similar issues arise with the contribution quests for war fronts.

We need to figure out a way to hide the quests when they aren't offered in game

Yes, I do not know what API to use to determine when those dailies, etc. are available.

Maybe https://www.curseforge.com/wow/addons/contributioneta/ can help with that.