Literary works are judged against the backdrop of their place and time. If a work is deemed "excellent" for its era, it remains so for all others; even if proven unworthy later, it retains its place in history as the once great literary work (the average personal library is full of has-been literature.) A work might increase in "excellence", if newer works reach back to it for influence, or if the work is deemed prophetic, predicting the norms and realities of a later era.