The Extension typically has the most up-to-date product data since sales estimates are fetched whenever you scan the page. We use the most up-to-date data points, process them through our estimation engine (AccuSales™), and return estimates based on that information.
Sales and revenue estimates in Extension (as well as the Product Database) are based on the ASIN's sales and revenue data from the last rolling 30-day period.
For example, if you run the extension to look at a product, the monthly sales estimate is not a forecast for how much it will sell in the current month, but an indication of how much it has sold in the last 30 days, regardless of where we are in the month.
If you want to learn more about how estimates work and how they are generated, we recommend reading our article on AccuSales™.