so for amex I won't get the bonus a second time
If I'm following correctly,
Your social allows them to pull your report if to accept/decline your application. The EIN tells Amex what business it is.
Bonus goes according to what you put into EIN number (NOT your SSN):
If you put in a different EIN each time you apply, then each business will get bonus (because that business never had the bonus yet)
If you enter same EIN/SSN, then after the first time you won't receive the bonus again because that EIN/SSN already received it