The point of the article is exactly that it isn’t 100% perfect and this slight imperfection has allowed companies like P&G to take advantage of that for large-scale privacy violation. From the article:

   The whack-a-mole1 aspect of Apple’s new privacy rules is that while Apple can restrict access to the API that provides access to the IDFA identifier, clever developers can find (perhaps infinite) other ways to combine things they do have access to into a unique, or even just “close enough to unique to be useful for tracking”, identifier. IP addresses, to name just one example, are a big factor that Apple can’t block would-be-trackers from using.