The clear issue around declaring it 'deauthorized' is that even those parties won't be capable of using OGC under the OGL 1.0a anymore because of section 9.
Where is section 9 of the existing OGL mentioned in the draft 1.2 document?
Here is the whole text of the notice of "deauthorisation":
The Open Game License 1.0a is no longer an authorized license. This means that you may not use that version of the OGL, or any prior version, to publish SRD content after (effective date). It does not mean that any content previously published under that version needs to update to this license. Any previously published content remains licensed under whichever version of the OGL was in effect when you published that content.
What is the legal effect of this? And what is the legal basis on which it purports to operate? I don't think it's clear.
For instance, it says that "Any previously published content remains licensed under whichever version of the OGL was in effect when you published that content." What is meant, in that sentence, by the verb "licensed"? What permissions are part of that licence?
To me, the most obvious way of understanding that notice is that it is a withdrawal of the offer to license the SRD on the terms set out in the OGL v 1.0a. This means, in terms of section 2 of the OGL v 1.0a, that the SRD is
not "Open Game Content that contains a notice indicating that the Open Game Content may only be Used under and in terms of this License." What effect does that have on existing grants of permission under section 4? I've conjectured some possibilities in the PSA thread, and you've read my posts. One possible construction is that it means the SRD is no longer the subject matter of the section 4 grant, as that grant is (on the conjectured construction) confined to OGC to which currently contains a section 2 notice.
I don't know if the preceding is the argument that WotC is relying on. They may have several in mind. It's the best argument that I know that gives WotC the result it wants - it confines the previous permission granted very narrowly, allowing existing works to continue to be sold but brining all future licensing of SRD OGC (including by way of sub-licences) to an end.
You are only allowed to use authorized versions of the OGL
If this is your interpretation of section 9, I don't agree with it. I can't see any plausible construction of section 9 on which it contains a power of revocation.
So deauthorization does invalidate the earlier explanation in the FAQ.
And? This has been discussed to death in many threads including the lawyer-PSA thread. I don't see how it bears on the point I was making, which is that WotC in its FAQ never said that the offer to license would not be withdrawn.