I can follow Thomas' thoughts here very well. this was also my doubt.
what do we have:
Sasama writes about such a smith, with no surviving works known.
the quality does not correspond with the early Soshu or Odawara works. (this kabuto here is better, smells edo)
what we also have, and this is quite unknown, also the Ichiguchi Myochin made this kind of kabuto during the early edo period.
the genealogy of the Ichiguchi is far from complete, It may be an unrecorded smith.
If it is the one mentioned in the SMZ, I think we have to wait till more kabuto pop up.
this kabuto has similarities with the late Soshu smiths. If it is one of them, it is certainly made after the troubled period of the battle of Odawara, wich was a turning point in the production of armor allover Japan.
I think we have to wait till more works from this smith appear, before we can be sure.