If WotC releases a revised SRD which contains X from the old SRD plus new Y; and then someone publishing under the OGL v 1.0a publishes a work that includes some of Y; that publisher might want to argue that Y is derivative of the old SRD and hence that they are not infringing, because licensed under the OGL v 1.0a.
I don't think that would work so I would advise the publisher not to include Y, to the extent Y is copyright protected material. Usually OGL publishers don't include big chunks of SRD anyway, they just want to be able to reference stuff like monster names & magic items.