Are new macOS versions retained in the recovery partition?
Found the answer to my own question:

The simple answer is, whenever you perform a major OS X upgrade, the Recovery HD partition is also upgraded to the same version of OS X. So, an upgrade from Lion to Mountain Lion will result in a Recovery HD linked to OS X Mountain Lion.

source: https://www.lifewire.com/identify-os-x-version-on-recovery-hd-partition-2259968