So prior One Tamriel I was able to enter the AD Harborage, and thus discover it. Now post One Tamriel, I'm unable to enter either the AD or EP Harborage's. Which does make sense to me and I don't think that is the issue.
But I can still fast travel to outside the doors of the AD Harborage, but cannot even discover the EP one (the icon stays black), more than likely because I cannot go inside.
So, this seems to me as a bug, if we cannot even discover the Harborage's of the other alliances, then should it stand to reason that they should not be on our maps? Otherwise, anyone who didn't discover it pre-One Tamreil, will now be stuck with a permanent black icon on their map.
Or, let us discover the location simply by approaching the doors of the Harborage, which is probably the easier way to resolve this in terms of the code. That way its a discovered location, just not one we can go inside of.