Permit Me One Qualm?

We can choose to switch from a presumption of innocence to a presumption of guilt if the priors merit it. However, regardless of which we choose, the presumption must be defeasible, at least in principle, yes? A charge which cannot, even in theory, be rebutted fails to conform to any reasonable definition of "due process".

What about a charge which may be contestable in theory, but is de factor uncontestable? I suppose it depends on your stance vis a vis substantive due process. If you're a pure, 100% formalist, you might very well say that the bar for due process has been met. But if you care about substantive issues you very well may object that a charge which, practically speaking, cannot be refuted fails that test as well.

Now, speaking more plainly to the matter at hand: How do we proceed if enough time has passed as to render relevant evidence inaccesible? Considerations of substantive due process might lead one to conclude that the condition of defeasibility has been violated, since one cannot, in practice, farily assess a charge without access to the relevant evidence.