In the first place, one can say it was essentially an invalid practice as it was no more than a private name between a vassal and his shugo daimyo, and was not under control of the Imperial Court.
そもそも、律令制の観点からいえば、これは朝廷の預かり知らぬものであり、守護大名とその家臣の間での私称に過ぎず、本来ならば不当ともいえる慣行であった。