Most of these "branded" cards will have an underlying issuing bank/acquirer, not their own identification on the card.

The way that the 16 digits are allocated is defined as per https://en.wikipedia.org/wiki/Payment_card_number#Structure

So of the 16 digits for the majority of cards:

Digit 1-6(8): Scheme and issuer identification Digits 7-15: Account identification Digit 16: Check digit (Luhn algorithm)

So most issuers have 10 digits to "play with" to identify the account.

So Japan is either running out of issuer identifiers, which sounds excessive, or they have been allocating them badly.