The first few, or all, purchases are likely tracked by Amazon to analyze for any trend. We already know from leaks that they track first show watched after sign ups so the first things purchase can be tracked. However that isn't important to linking books sales to the show. What do you think would have created a large increase in book sales at the same time that Rings of Power came out? What else was happening in regards to Tolkien or Lord of the Rings to see a sudden increase in sales?
You act as if Amazon is dumb and doesn't have servers full of data to analyze these things. The only thing coping is yourself and it is amusing that you can't actually see that.