Nether Portals built outside the detection range of existing overworld portals do not generate a new nether portal within the Nether dimension after a singular nether dimension portal has been created once.  All new portals created in the overworld link to that singular portal until a portal is manually created by a player at the appropriate location to link, and not to a portal at their respective 1/8th distance x,z location.   

The reverse is also true -  manually made Portals in the nether do not generate new portals in the Overworld if the portals are outside the expected radius for existing portals.