The explainee's problem is to explain C (he has absolutely nothing else to work with)! It is an unstated assumption in any scientific work that the best explanation of C (the information you have to work with) is an explanation of A (the source of the elements which make up B the things you can test). Certainly there is no proof that A can be explained; that would require knowing A in it's entirety (in which case, there is no information in A not seen in C). But that is impossible as the possibility always exists that another B exists (by definition you cannot examine an infinite set).

My model always explains C (I give a specific finite procedure for generating that explanation). So there is nothing you can know which cannot be explained no matter what the demon attempts. The demon can not create a universe which cannot be explained. The whole story is in the interpretation of the meanings of the elements of C.

Dick