How do chase and amex decide if you have the other's card before?
 

How do chase and amex decide if you have the other card before, in order to deny you a welcome bonus?

1, compare SSN you filled in the application. I don't think they are allowed to disclose this information to a third party.

2, through marriott number. But one can just not fill it in.

3, check credit report to find out what card you have. But the credit reports don't show full credit card number. Even the partial number is not the same with you true credit card number.

4, direct communication with each other "hey chase, this guy with name, birthday, and address just applied for a marriott card with us. please check if he got one from chase before." I dont' think this one is allowed as well.

It seems only 2 is doable, yet easy to get around with. But even then, since chase need to decide if one got marriott upgrade offer within 24 months. This seems to require information from amex. I find it hard to believe chase and amex are allowed to exchange that kind of information. The only possible way I can think of is to let marriott to decide. Since marriott have the inforamtion of when one received welcome or upgrade offer from both amex and chase, when the corresponding points post, they can decide if to issue welcome bonus or not. This seems to be the only possible scenario. Yet, will marriott be able to know if someone has Amex spg card within 30 days? If one close the card, will amex inform marriott within 30 days? Maybe.

But then, one can simply not fill in marriott account number at application. Chase will create a new one for you. I am not sure if Chase can release your birthday and address to marriott. Even then, you can change your address in the marriott account to a different one. I don't really think marriott will extensively check if someone has a account with them before, unless one require to combine accounts.

Any DPs and thoughts?

How would you expect to obtain a Marriott-cobranded card (and receive a welcome bonus of Marriott points) if you don't include your Marriott Bonvoy account number on the application?

Per FT Rule 6, posts should not be cross-posted. Given this topic has a wider context than specifically Marriott alone, this thread will be closed and further discussion can continue in the https://www.flyertalk.com/forum/american-express-membership-rewards/2012991-how-do-chase-amex-decide-if-you-have-other-card-before.html thread.