Are Recovery Keys unique to an OS install?

If I reinstall Server 2012R2 Essentials from scratch (e.g. from the WD-provided recovery image, written to a bootable USB drive) and then reinstall all my clients, can I still use a Client Recovery Key USB drive that was created from the previous install to recover a client PC?

Or are the recovery keys tied to some sort of GUID that’s created at OS install time?

The recovery thumb is not tied to anything, but it does change with windows updates sometimes. I would make a fresh one or use the PXE boot option if your clients support it.
Still Grey

I love NetBoot! When it works. Even if it’s slower it’s just the neatest thing to show people.

But not all my clients support it.