As a minimum requirement the article requires wholesalers to verify the authenticity of the UI for at least the medicinal products in his physical possession which are

• medicinal products returned to him by persons authorised or entitled to supply medicinal products to the public or by another wholesaler
• medicinal products he receives from a wholesaler who is neither the manufacturer nor the wholesaler holding the marketing authorisation nor a wholesaler who is designated by the marketing authorisation holder, by means of a written contract, to store and distribute the products covered by his marketing authorisation on his behalf.

A wholesaler may verify the authenticity of other products of other origins than those addressed in Article 20 via the UI when the product is not in physical possession. This should be considered an additional check. It does not exempt from the obligation to verify the UI once the product is in physical possession and can thus not replace it. Only authorised suppliers located in the EU can put medicinal products on the market in the EU. Verifying the UI of packs located outside the EU does not replace import testing and batch certification after import by authorised manufacturers.

Source:
EC: Q&A on safety features for medicinal products for human use, Version 20