The same is true of most genres of music that were really popular during a specific time period. Punk rock arguably was constrained to the late 70s, but you can

The same is true of most genres of music that were really popular during a specific time period. Punk rock arguably was constrained to the late 70s, but you can still find artists who are arguably punk rock. Genres are a fuzzy classification and time periods are not really the best way to nail down a genre. I guess it sort of works to identify the start of a genre (if you ignore a couple of outliers like Gesualdo who was doing Chromaticism waaaay back in the Renaissance period) since artists copy each other (and copy general trends), and technology / theory can also be a component. I guess you can tentatively identify a beginning of an artistic movement. But an artistic movement only really dies when no-one cares about it, at which point no-one really cares when it finished.