Just to add to this: OGC is not a label that pertains to certain copyrighted material in virtue of its content. It attaches to that material in virtue of its status within a particular contractual licensing regime. WotC's publication of the rulebooks that you mention has nothing to do with that regime.No, the material as presented in the PHB, MM, and DMG is not OGC. You can't source it from there. It can only be sourced from the SRD.
This creates interesting theoretical questions. Suppose (i) I reproduce a section of the SRD that is OGC for which a licence in terms of the OGL is offered by WotC, as per the notice affixed to the SRD, and (ii) the particular bit of the SRD I reproduce is also found word-for-word in one of those rulebooks, and (iii) I don't include a copy of the OGL in my work, nor a clear notice as to what in my work is OGC.
In that scenario, am I infringing WotC's copyright in its rulebooks? Or breaking my contractual obligations under the OGL? Or both?
I think - without being definite about it - that the answer depends on the factual question of what my intentions and beliefs were when I reproduced the text. If I believed I was entitled to do so by the OGL, and that I was exercising permissions under a licence granted by WotC, then I think that (at least) I'm in breach of contract. If I was ignorant of WotC's offer to license the work under the terms of the OGL then I don't see that I can be in breach of contract, and my liability is confined to copyright infringement.
I describe this as a theoretical question because I can't imagine a practical context in which this would not be resolved via negotiation between the parties, with the upshot being either the withdrawal of the offending work (perhaps with a payment to WotC also) or else a cure of the work as envisaged in section 13 of the OGL. (Assuming that WotC accepts that the OGL remains effective in respect of its SRD content - so let's suppose my example is occurring a couple of years ago!)