The unwritten rule that, after a given number of years, there has been enough turnover in the fanbase that a writer can re-use the same gimmicks and storylines with impunity. The general principle applies to any work that is enough of a Long Runner and/or has enough of a Fleeting Demographic to outlast most of its initial fanbase. Compare Recycled Script. Contrast Spiritual Successor where the writers don't have to pretend this isn't a rehash - because it isn't truly a rehash. Examples of Fleeting Demographic Rule include: