This is valid, with a small "but":
As soon as Windows 10 version 1511 or later is activated, regardless of the activation method or product key type, it is entitled to digital activation and license.
Therefore, the product key or other activation methods are not (should not be) needed when re-installing Windows.
Version 1511 always shows the product key after initial key activation. It is of course already entitled to a digital activation and license but that will only be shown after first reinstall without a key.
1607 made this a bit easier to understand, showing Digital License instead of Product Key already after the initial first product key activation.
See my reply above