I just think that there are not as much string manufactures out there as we think.
In the '80s Ernie Ball strings WERE D'Addario. Not made to Ball's specs, the same strings. The entire line, guitar and bass. EB was D'Addario's west-coats warehouse, strings were exactly the same, etc. Even the gauges of individual sets.
At that time in the US it was pretty much D'Addario, GHS, Squire (owned by Fender), Darco (owned by Martin I believe), NMS (Kaman), Sterling worth (now apparently owned by Dean Marley), and LaBella. Maybe a couple others.
John