I don't understand. If they offer any sort of GPL on their code, irrespective of some other license also placed on it isn't a user entitled under such AGPL to f

I don't understand. If they offer any sort of GPL on their code, irrespective of some other license also placed on it isn't a user entitled under such AGPL to fork it as they please, where continued free (as in freedom) use and subsequent further forking can take place?