Yesterday, Apple’s Environment – Answers web page contained this sentence:

Years of use, which are based on first owners, are assumed to be four years for MacOS and tvOS devices and three years for iOS and watchOS devices.

Note the reference to MacOS. If you visit the page today, you’ll see that MacOS was changed to read OS X.

Back a few weeks ago, another mention of MacOS was discovered buried in some library files, joining another buried MacOS from last August.

This is speculation. But mounting speculation.