As for koban (former Japanese oval gold coin), the karat was upgraded a little when shotoku koban was changed to kyoho koban, and there is a theory that the karat of chogin was also upgraded in the early stage to keep a balance with gold coin.
尚、小判については正徳小判から享保小判への変更に付き若干の品位向上となったが、丁銀についても金貨とのバランスの関係から初期の頃に品位を若干向上させる変更を行ったとする説もある。