I have to agree with milt, looks like a later add-on or "attribution"
to Masanobu of the Bushû-Itô-branch. He is listed in "Sôken-kishô"
(装剣奇賞, publ. 1781) as signing with kaô. Probably this kaô was
made just to look like a kaô.
See also Tôken-bijutsu 12-2006 (599), page 20.
BTW: Regarding the attribution, motif respectively workmanship
could match.