Ink can fade or be made to disappear, adding urgency to reading. Digital text and images can be erased and altered giving lie to memory and reminiscence: counterfactual.
Changing states of readability are built into the technology of publishing. Paper turns brittle, yellow, crumbles, becomes dust. Bindings and glue decompose, are consumed by animal and vegetable parasites.
Orthography and spelling changed by habit or decree is accurate like carbon dating. Words lose meaning, change use, shift to other registers of respectability and acceptance, going over the top, a bit too far, beyond the pale, out of order.