Most of your items do show that you ship internationally with the gsp but for those listings the shipping price to those countries would already show. If the buyer doesn’t see a shipping cost to their country then the gsp doesn’t ship that item there so you can tell the buyer that.
To prevent buyers from buying even though there are no shipping costs specified to their country you should go to account, site preferences, buyer requirements and check off to ‘block buyers with a primary shipping address in a country that I don’t ship to’. The listings with the gsp will still have the gsp on them but if the gsp doesn’t ship to that country, they will be locked from buying. It will also block buyers from buying non gsp listings unless they have a US address.
