Regardless of what the sayagaki says, I would not get my hopes up thinking this tanto was made by Hasabe Kunishige or that it dated to the Nambokucho era . Much more likely that an inaccurate saygaki was written by someone, perhaps believing the attribution, perhaps intentionally to increase perceived value.
I see a number of inaccuracies which do not match Kunishige's work.
Their tanto were slight saki-zori, this one is slight uchi-zori.
There were schools which produced Unokubi-zukuri tanto during the Koto period yet, Hasabe works were not known for forging unokubi-zukuri as this one is on the ura side.
Kunishige forged tight itame with masame along the mune with lots of chikei and ji-nie. I see no hada at all.
Due to the masame, his hitatsura was more vertical than horizontal as in this example (see photo).
There ia a visible ha-hada in shoshin works (see photo).
The nakago was funagata (see photo).
My guess is that this tanto is shinshinto attempting to pass as Hasabe Den.
In shinshinto period the hada had become muji ie; so refined its barely visible to the eye.
Unokubi-zukuri had regained popularity during this time.
Understand this is only my opinion, others may disagree.
For a better, more accepted opinion, there will be a NTHK shinsa this June in Florida.
Being mumei, it will paper to someone if the polish is sufficient to judge.