this is too much getting into details to me .... i dont think that u HAVE TO have a can to do graffitti. and also stencils are not necessairily something different. some graf heads used stencils and masks 20 years ago for their pieces of for some of its details ... stencils are nothing new, and were - for example - largely used in the 80ies skate designs ... there just wasnt any media to label us as skate art.
i see graffitti rather as a way of expressing yourself ... no matter if u spray or paint ur pic or ur message.
the (french speaking) board members might remember the film "la haine" where they show a poster saying "le monde est à vous" (the world is yours) and they sprayed over the "v", so it says "le monde est à Nous" (the world is ours). to me, this is allready graffitti.
don't forget that graffitti is a part of hiphop, and hiphop is about uniting things, not separating them into different drawers ...