How is it even possible for A and B to be indiscriminable, B and C to be indiscriminable, but A and C to be discriminable? It seems like if A and B cause the exact same conscious thoughts (or whatever you're updating on as evidence), and B and C do, then A and C do. I think in practice, what's more likely is that you can very weakly probabilistically discriminate between any two adjacent states.
Frank Arntzenius (a philosopher at Oxford) has argued something along these lines.
I don't think that article is paywalled (though I'm using a university computer, logged on to my account so I'm not sure whether I automatically get passed through any paywall that may exist).
If it's worth saying, but not worth its own post, even in Discussion, it goes here.