I recall Apple saying that they won't store ApplePay customers' purchase history or credit card information on its servers and that the ApplePay-accepting merchants will not be able to see ApplePay customers' credit card numbers but that those merchants will get an Apple transaction number and the payment from ApplePay. And I've not yet seen anything that indicates it to be otherwise.

Amex, on the other hand, definitely stores purchase history on its servers; and that purchase history stored by Amex on servers can and will be used against customers at times. I am curious how reliably it goes with making an ApplePay purchase with an Amex card at a merchant but then the buyer returning the purchase for credit to a non-Amex card linked to a given ApplePay account. Amex would have the initial purchase transaction, but would it have the refund transaction data?