The 1-, 5-, 10-yen have always had Japanese–only dates. The regular issue 500-yen also, which is a somewhat newer coin, began in 1982 with a Japanese–only date.
The nickel 50-yen and the silver 100-yen began with Japanese–only dates. But for some reason, beginning with the 1967 issues in copper-nickel, 50- and 100-yen coins have their dynastic dates rendered in Western–style numerals (I note the 1964–regnal year 39–Olympic 100-yen commemorative in circulating silver also had Western–style numerals in the date).
If someone can explain this duality in Japanese coin-dating, I would appreciate learning the reason.
