how to determine sales volume for varations

Hi All, I am trying to figure out what the best method is to determine the sales volumes for varation listings. Softwares such as jungle scout or seller amp rely on reviews and other data. But I think they may not be accurate, what about the sales volume number on the product page that amazon provides, does anyone know how accurate that is ? I have attached a snip where amazon data shows 2K bought for black version of an item and when I toggle between the two variations the data changes.