I have not used KDP at all - but I have noticed that a spike in free downloads of my first book (which is free on Amazon) does not show in sales till the NEXT month. So while my "sales" rank might jump with the free book (seen it jump several thousand in a day), I see no change in PURCHASES of my second book till the next month.
Currently I get around 1 purchase to 10 free downloads. I suspect I will see a spike when I release book four... soon, and hopefully very soon!
Since I do not use KDP I do not have "free days" to worry about. My first book is always free. That might change the dynamic a bit. I am not sure. I am just guess my way through this book thing.
