stock problem: last modification date product with sale

in Development
i update my product through the api, based on the last modification date
i get the stock values by ["Item"]["ItemShops"]["ItemShop"][0]["qoh"];
but when there is an in-store sale, I think it does not change the last modificated date of the product
so i do not get an update on the stock of this product with the api
any idea what i'm doing wrong?