How to best add rulers to Japan?

There are a lot of Japanese coins without a ruling authority and I want to propose some ruling authorities, but I'm not sure how to best go about it. I see 3 options:

Devided by Period, like Edo

Devided by Era (which was not determinated by the emporor before the post Edo period)

Devided by Emperor, where coins will overlap a lot with different emperors.

I'll like to know what people think, or suggest since I think there can be different opinions on what fits best?

For consistency the emperors should be used, but if they should be more fitting for the items' it should probably be by eras..?

Coins missing rulers:

https://en.numista.com/catalogue/index.php?e=japon&r=&ct=coin&im1=&im2=&tb=y&tc=y&tt=y&cat=y&ru=missing&ca=3&no=&v=&i=&b=&ie=&u=&a=&dg=&m=&f=&t=&w=&mt=&g=&se=&d=&c=&wi=&sw=&o=y

The rulers we have now (the space means missing ruler(s), but not all may have coins in that period), with the oldest coin missing ruler from 890-907:

Genmei (707-715)

Junnin (758-764)

Shōtoku (764-770)

Kanmu (781-806)

Saga (809-823)

Ninmyō (833-850)

Seiwa (858-876)
 

Murakami (946-967)

Go-Yōzei (1586-1611)

Go-Mizunoo (1611-1629)
 

Nakamikado (1709-1735)

Go-Sakuramachi (1762-1771)

Go-Momozono (1771-1779)

Ninkō (1817-1846)

Kōmei (1846-1867)

Meiji (1867-1912)

Taishō (1912-1926)

Shōwa (1926-1989)

Heisei (1989-2019)

Reiwa (2019-date)

Wiki list of period, era and emperor names:

https://en.wikipedia.org/wiki/Japanese_era_name

Here is a Google Doc link with a list of Japanese Emperors and there status in Numista's database right now.

Google doc link

It's not always easy to point specific people to one coin because we still have many clustered coin entries because of the nature of the Kan'ei Tsuhou issues being very similar to nearly identical and issued over centuries.

A further point is the issue that Emperors in large parts of Japanese history are just figure heads and the shogunate is the de facto ruling entity and also in charge of the issue of coins and later scrip but the names of emperors being most often the standard in reference material. List of Shoguns

Another question that I have asked myself for many years now. Many English sources use the names of Emperors not their nengō for example Naruhito instead of Reiwa (he is still living after all), a bit more complicated Hirohito instead of Shōwa and strangely not true for Taishō or Meiji (Yoshihito and Mutsuhito). Should we keep it how we have it right now or change their names?

Rather than dividing by emperor, how about dividing by era such as the Edo period or the Heian period?

I think many currencies will become easy to understand groups.
I don't think I'll be familiar with it, but I think it will be refreshing.
I feel that the Edo period, which lasted a long time and produced many coins, is very difficult to read.

Although there are some parts that are unclear, I think it is best to use common ones. There were no coins in ancient times, and coins were imported for a long time, so I think it's enough to know about the Edo period and before. Sometimes there are two emperors.

I propose the following classification. I think this will make the page easier to read because there will be fewer partitions and more relevance. I would appreciate it if you could consider it.

Nara and Heian period(奈良及び平安時代)

710-1192

(Nara:710-794，Heian:794-1192)

Since Wadōkaichin to Kengen Taihō are treated as one group (in Japan), I have classified Nara and Heian as one category(kōchō jūnisen).

In Japan it is called 皇朝銭、皇朝十二銭(kōchō jūnisen).

https://ja.wikipedia.org/wiki/%E7%9A%87%E6%9C%9D%E5%8D%81%E4%BA%8C%E9%8A%AD

Azuchi-Momoyama period(安土桃山時代)

1573-1600

Edo period(江戸時代)

1600-1868

Meiji、明治 (1868-1912)

Taisho、大正 (1912-1926)

Showa、昭和 (1926-1989)

Heisei、平成 (1989-2019)

Reiwa、令和(2019-)