Millions will know which items are scanned. If the customer purchases the item before the item to scan people counting sales before core-quarter make the cutoff is correct.
People are aware that the items are scanned so far. If a customer bought a product before a scan counts are scanned before the cutoff for making accurate.
Hundreds of products will know that any product scan. If the products customers buy before scan hundreds of items are scanned before sale makes the cutoff correctly.