Deterrent buffeting should, as its name infers, deter you from trying to pull any harder or fly any slower. I would assess deterrent buffet as a motion (usually a vertical bounce) harsh enough to cause discomfort to the crew which usually makes reading the instruments difficult (or impossible!). The Hunter T7 displayed a harsh vertical bounce which could be called deterrent buffet whereas a PA 28 just displays gentle buffet. To get the aircraft to stall the aircraft has to be flown through the buffet until a defined stall occurs. I no longer have access to Def Stans, but one definition of a stall is an uncontrollable nose drop - I am sure there will be others who can offer other definitions.