Truth to be told, I would personally find interesting to add to the database all the demos, at they are still a downloadable and a playable content from the Store. We could argue that it is more important to preserve and document them than to preserve the Youtube app, as the demo is the one that is the most game-like if you could say that.

As long as a release is important enough to warrant a dedicated serial number. I feel like it need it's own entry in a database that wants to be complete, at least as much as DLCs.

But it's only a personal opinion of course, you're the one that created and maintain the database it belongs to you to decide that. The work you've done so far really is incredible. You are the one that should decide (and it would be a fucking long work).