These are most likely sales made in stores worldwide. International stores actually provide their sales data a month later, that is, at the end of the month following the reference month.
- The sale happens in February
- The international store reports it to us at the end of March
- Only then is the sale reported in our Analytics area as described here.
Some examples of international stores: Amazon Kindle Store, Apple iBookstore, Google Play Store, KoboBooks (who also runs the digital catalogs of InMondadori and La Feltrinelli), Nook Store, Tolino (who also runs the digital catalog of IBS), Barnes & Noble, OverDrive, Scribd, 24Symbols.