Uma Musume: Cinderella Gray - Vol. 17 Ch. 147 - Once Again

[Sleabedybarb]

that rule was on G1s rather than classics iirc. There's still limit. it's why Digital managed to run akiten and Kurofune didn't.

Eishin Flash per registry is a JP horse so by birth, he's eligible to enter without fuss. Maruzensky's case was a far more discriminatory rule which resulted into Maruzen only managing to race eight times because no one also wanted to race against him.

Digital and Kurofune were both born in America, and Kurofune didn't run in that race because he had already switched over to dirt by then
and no, Maruzensky was a JP horse by birth, it's the exact same situation as Flash:
https://en.wikipedia.org/wiki/Horse_racing_in_Japan#Restrictions