FYI this also affects the apparent ownership on the amazon product page, for some reason. At least it does for me, and only for these 4 volumes. On both the series summary page https://www.amazon.com/dp/B0GQ9QWL7F , and on individual pages such as https://www.amazon.com/gp/product/B0GLYR5FTV it gives me the option to buy the kindle version - the button says "Buy now with 1-Click" instead of "Read Now".
But when I open my actual Kindle app of course, I own those 4 volumes already and can read them. They are just not grouped in the series with the rest of the volumes.
So as it is now I could accidentally buy the book a second time, though I have not tried to.