Good Evening @Seller_CkGirf8tRNDyo,

You will find more details about "bought in past month" in the Sales Trend FAQ page. Sales trend helps customers differentiate products in Amazon’s vast catalog by providing a broad estimate of the number of customers who recently purchased a product (for example, "10K+ bought in past month"). Sales trend data is refreshed at least daily and does not include returns and cancellations. Sales trend cannot be turned off, and helps customers make more confident purchases, which can help drive an item’s popularity and visibility in search rankings.

For the question around the API, you can check with Selling Partner Support if it is not answered in the help page. Hope that helps answer your question. Have a great rest of the week.

Sincerely, Cooper_Amazon