These bands you mention are called here `proto-underground`. They are more than speed metal but not quite death/black metal. Thrash is stuff like DRI, Corrosion of Conformity, Cryptic Slaughter etc., the so called crossover bands. Sarcofago is close to this, you could legitimately call it thrash by the standards here. It doesnt really deserve much fuss to be honest, even if almost everyone calls speed metal thrash and even if it produces confusion and odd rationalizations, it only matters as far as consistency of definition is concerned. That is not unimportant, but it is much less important than promoting quality, whatever it is called.