Over a month after the release of macOS Sierra 10.12.4, Apple quietly let slip the news that it changed macOS Recovery modes, including the startup key combinations used to enter them. Full details are given here, in a Knowledgebase article dated 3 May 2017.

If your Mac is running a version of macOS/OS X prior to 10.12.4 and supports Recovery mode, the available modes and their reinstall behaviour remains unchanged:

• start up into local Recovery mode using Command-R, and if you reinstall macOS you will get the same version as is currently installed on your Mac;
• start up into remote Recovery mode using Command-Option-R, and if you reinstall macOS you will get the original version which shipped with your Mac, and will then need to update that to any later version.

There are now effectively three different Recovery modes, which behave differently depending on whether your Mac is running macOS 10.12.4 or later:

• local Recovery mode, engaged with Command-R, behaves as before, and if you reinstall macOS it will provide the version which was running on your Mac, even if a more recent version is available;
• remote latest Recovery mode, engaged with Command-Option-R, behaves differently according to the version of macOS installed. In 10.12.3 and earlier, reinstalling restores the version which came with your Mac. In 10.12.4 and later, reinstalling upgrades your Mac to the latest version of macOS which is compatible with it.
• remote original Recovery mode, engaged with Command-Option-Shift-R, only works if you’re running macOS 10.12.4 or later. If you reinstall macOS from that, you will get the version of macOS which shipped with your Mac.

Apple also warns that not all old versions of macOS / OS X may be available to reinstall, and the version actually installed may be “the version closest to it that is still available.”

The whole point of Apple’s article seems to be directed at those reinstalling macOS prior to selling or otherwise disposing of their Mac. It draws attention to the recommendation that, when parting with your Mac, you should use the Command-Option-R remote latest recovery mode to reinstall macOS if your Mac is still running El Capitan or earlier, to ensure that it is not associated with your Apple ID.

Even Recovery mode, once so simple, now seems to need a day’s training course to understand its new Byzantine complexities.

Thanks to Bob for drawing attention to this change in a comment on this blog.