Thanks again.

I accepted both (i) the payment debit from the linked Chase checking account, which was paired with the primary Chase credit card (Card A) sub-account and (ii) the payment credit to the Card A sub-account.

I then created two transfers of the allocable portions of the resulting Card A overpayment to the sub-accounts for Card B and Card C.  All three cards now show the correct QB balances.

So it appears that when I pay the total credit card balance each month I'll need to manually transfer any resulting overpayment of the primary card to the other sub-accounts.  It would seem that Chase and/or QBO could make this a bit easier.  (For example, QBO could allow you to readily split a credit card payment amount sub-accounts when you accept the transaction.). But until then, this seems to be a work-around.