What DAWs use to differentiate plugins?

Developer VST 3 SDK
2

Each VST3 plugin is identified by its UID defined in the processor component not by its name or filename.

BEGIN_FACTORY_DEF ("Steinberg Media Technologies", 
			   "http://www.steinberg.net", 
			   "mailto:info@steinberg.de")

	//---First Plug-in included in this factory-------
	// its kVstAudioEffectClass component
	DEF_CLASS2 (INLINE_UID_FROM_FUID(AGainProcessorUID),
				PClassInfo::kManyInstances,	// cardinality

here it is AGainProcessorUID