How can I preserve bundled digital games that came with a used Wii U?

Question

I recently bought a second-hand Wii U off of eBay which came with a few games, some digital and some physical discs. The intent of buying the machine was to not only have an HDMI capable machine for my Wii collection, but also to run my GameCube discs on HDMI via Homebrew hacks.

I noticed that the non-browser based hack injection requires a game to be bought from the Wii U eShop. For that, it would obviously require a linked Nintendo Account ID (NNID?) and I have one for my Nintendo Switch, but no other Nintendo machines. From what I've read, it seems that once a Wii U has been associated with a NNID, you cannot associate that Wii U with another NNID.

Now it would be trivial if I just did a "wipe all settings" to start fresh on the Wii U, but since two of the games that it came with are digital (it was a Mario 3D bundle machine), I'm concerned that I might lose the digital games.

So my questions are:

1. Validation of the assumptions above.
2. I don't believe the Wii U was ever associated with an NNID as there is only a 'guest' account on it and going into its details I can see that it is asking me if I want to link it to a NNID which I'm assuming means it never was linked.
3. In its current presumably anonymous (non-NNID-linked) state, would a "wipe all settings" preserve the digital games? i.e., are they burned in the machine or re-downloadable based on the machine serial number? Or do I need to associate an account with my NNID before I attempt such a thing?
4. Given that the machine is several years old, is it too late to do such an action?

Thanks!