Certainly. I am suggesting that over sufficiently short timescales, though, you can deduce the previous structure from the current one. Maybe I should have said "epsilon" instead of "two words".

Surely there's been at least a little degradation in the space of two words, or we'd never forget anything.

Why would you expect the degradation to be completely uniform? It seems more reasonable to suspect that, given a sufficiently small timescale, the brain will sometimes be forgetting things and sometimes not, in a way that probably isn't synchronized with its learning of new things.

So, depending on your choice of two words, sometimes the brain would take marginally more bits to describe and sometimes marginally fewer.

Actually, so long as the brain can be considered as operating independently from the outside world (which, given an appropriately chosen small interval of time, makes some amount of sense), a complete description at time t will imply a complete description at time t + δ. The information required to describe the first brain therefore describes the second one too.

So I've made another error: I should have said that my brain contains a lossless copy of itself and itself two words later. (where "two words" = "epsilon")

I never meant to say that I could give you an exact description of my own brain and itself ε ago, just that you could deduce one from looking at mine.