I have personal data on this. One account number is good. And better.
My husband had an Amex Airmiles Platinum card. We directed the 2,000 Airmiles sign up bonus to his Airmiles account. He referred me to the Amex Airmiles Platinum card and got 500 bonus Airmiles for all his trouble (tongue in cheek). Those bonus miles posted to his account. I entered his Airmiles number in the application and my welcome bonus posted to his account. 4,500 Airmiles!
On that note,
Please stop wasting referral opportunities. It's an easy 500 Airmiles for the person referring. And can be carried forward. If anyone needs help, I'd be happy to walk you through it.