While I can't tell Apple they did the same for classic MacOS, for the latter they did provide guidelines for developers about their design philosophy and while

While I can't tell Apple they did the same for classic MacOS, for the latter they did provide guidelines for developers about their design philosophy and while OSX changed visually over the years, for most of the part it works in same way - controls, widgets, buttons do the same. Microsoft tried doing same thing around Vista but they never managed to keep following own rules and OS, Office, Windows Live software releases were always split apart in terms of how they look and work; this still happens even today - Metro interface still shares the ground with classic elements. Not mention that deep beneath all visual changes they made in last 18 years there are still resources dating 9x/NT times.