Any blades under 15 cm do not have to be registered except daggers. Daggers over 5.5 cm are always illegal. Usually, a kogatana does not need to be registered only because its blade length is less than 15 cm. There is no description of mekugiana in the Act for Controlling the Possession of Firearms or Swords and Other Such Weapons.
1. 遠見松透 紋造作 – Openwork of a view of pine trees, Monzo made.
平成壬申五月日 – Heisei mizunoe-saru (1992), 5th month
紋造作之 – Monzo made this.
2. 太刀透鐔(甲冑師) - Tachi sukashi tsuba (kacchushi)
甲戌作之 – Made this in the year of kinoe-inu (1994)
紋造 - Monzo
Frankly, I do not know how to explain more than my previous comments.
I said that the first day of Koka era is Koka 1st year, 12th month, 2nd day.
So naturally, Koka 1st year started on the 2nd day of 12th month and ended on the last day of 12th month. The following day is Koka 2nd year, 1st month, 1st day.
How can Koka 1st year, 2nd month exist?
I do not understand what you are saying. But anyway, the first day of Koka era was
Koka 1st year, 12th month, 2nd day (Lunar calendar in Japan at that time).
The day is equivalent to
January 9, 1845 (Gregorian calendar), or
December 28, 1844 (Julian calendar).