My first thought is that WotC has a contractual relationship (licence) with A which permits A to issue sub-licences, and then you have a contractual relationship with A which also establishes the sub-licence. Because I don't think you've taken up WotC's offer, you've taken up A's.It is early in the morning for me & I'm still sleepy, but I think if I take material from say The Hypertext d20 SRD (v3.5, 5e & Pathfinder d20 System Reference Document) :: d20srd.org under the OGL I would be held to have a contractual relationship with WoTC, as well as with the d20SRD.org people, and with everyone else whose d20 game material I took. I think this is what Umbran means by calling the licence offer non-revocable.
But you think I'm wrong?