What I've got in mind is that material found in a revised SRD (say, a new way of describing Elves) might be (in some fashion) derivative of material found in the 5e SRD (say, the existing way of describing Elves) and hence be something that the existing licence permits an existing licensee to use as OGC.
If you use the OGL & 5e SRD you can use the contents of the 5e SRD plus any non-copyright-protected material/concepts in a later SRD. You don't gain any special rights over material derivative of material in the 5e SRD afaics, if that material is independently copyright protected. The normal rules for copyright protection apply to derivative works. If I have a licence to use copyright work A, and B is a copyright work derivative of A, the licence to A doesn't give me any right to use B.