The first advice that we can give you regarding making product level or material level claims, is to familiarize yourself with local regulations regarding consumer facing product claims in the markets where you are selling.
Second, when communicating impacts it is always important to make sure that the impacts that you are communicating, match with the product or material that you make the claim about. This sounds logical, but can be tricky! It concerns being precise and accurate about which life cycle stages have been taken into account when calculating impacts.
The MSI only takes into account cradle-to-gate (textile processing) impacts and hence MSI-impacts are not fit for communicating on a product-level. You need to use the PM to determine impacts on a product level. Use PM-impacts to communicate about the impacts of an apparel (or other type) product, and use the MSI to communicate about the impacts of a textile (or material).