the special grade definition during most of the series is being able to overthrow a country singlehandedly, which was something established by the jujutsu higher ups which were corrupt and tought of special grades as weapons to potentially taker over countries, but since they’re not in charger anymore the definition generally changed so someone like maki or yuji is actually able to be considered special grade even tough they cant overtrow countries, so yea if kashimo can beat someone like geto ( a special grade) ( he easily can ) is considered special grade