I am an AU on AMEX BCE. I tried to apply for AMEX Green & Delta. Both were denied saying my scores are too low. Both time i was above 650. So scores of lower 600 is absolute denial AMEX.
BTW, they hard pull for AUs. That Soft Pull thing only works for Primary account holder. For AMEX DELTA they pulled all three bureau reports.
I've been an authorized user on an AmEx card for about a year and a half. Always pay in full, it has a high CL. My scores are in the low 600's. Will be chances be better forming my own relationship with Amex? I'd like to app for the Gold Card once a few more negatives drop off next month. I've heard of people being approved with scores right around 600. I should have jumped on the Zync bandwagon while it was still there!
In addition to FICO scoring, Amex uses their own Internal Scoring System. Its possible to get a charge card with a score of around 600 or so. There are alot of factors they take into consideration.
What is your credit profile like?