Depends on what you mean by the bold...
Score, Number of Accounts, Total Credit, Length of Credit, etc.
I am assuming that if you remove said person as an AU then the AMEX account will just drop off their Credit Report as if it never was there as they were not a "Responsible Party" correct?
Theoretically? Probably. (on an additional cardmember, NOT AU)
I still haven't been able to get a rep who can diffrentiate between an AU and Additional Cardmember. They keep telling me there are only 2 types, Joint Cardholders and Authorized Users which are sometimes called Additional Cardholders...