I understand what you’re talking about, I’m trying to tell you how it works.
So if I donated to a browser game without downloadable files (or a free game with files), and the game later gets a dl version added and is changed to a paid game, it should appear under purchases and I would have access to the files.
It does not. This scenario is a special type of purchase that does not generate any “download key”, so it will not appear in your library as an owned product.