I have noticed reporting lags in free downloads, and I think they comes from several sources. In some cases, a book is not "sold" until the buyer turns on his or her Kindle and updates, so someone browsing books on a desktop may make a purchase or free download that is not reported for several days. I also think there lags in reporting downloads from some European locations. When I have had really big promos (10K+ downloads) it is usually 4-5 days later before the numbers stop going up. I think this is normal.