like thrombin-stimulated platelet, or collagen-stimulated platelet...should the drug be effective on all of them or it would still be considered effective if it only worked on one of the stimulated platelets?
An effective anti-platelet drug should prevent thrombosis and
not induce bleeding. If you inhibit platelet activation by several agonists that are necessary for haemostasis, you will see bleeding.
There are new anti-platelet drug in the pharmaceutical pipeline that might help to fight thrombosis but do not induce bleeding, as Revacept or inhibitors of VWf-platelet GPIb interaction.