Most important, sco charter cares now the present time not the past, as such pakistan doesnt violate sco charter now, but india does by being in a group quad that is designed aginst china and russia.
Frankly, i dont know why you india want to be in sco since you want to be in quad that is designed against sco members while sco is designed not against anybody. The only reason you indians want to be in sco is to sobtage it, thats the only reason i can think of.
Pakistan doesnt have an agenda with the us as a group that is designed against other sco members, but you india does by being in quad.