After learning about Amex's backdating policy, I have the following question. Say I were to add someone with basically no credit history as an AU on my Amex card, and then one year later that person applied for their own Amex CC, would Amex then backdate their card to the year that my card was started (which they are an AU on)? If they would do this, and after that person activates their own card, would removing them as an AU on my card then affect their start/membership date on their own card?
It seems there are glitches in the system, but I believe the standard AmEx policy is that the AU would be a "member since" the year they are added as an AU.
They then "own" that "member since" year and it follows them on any subsequent accounts, whether they remain an AU on your card or not.
Some folks have had different experiences, including the backdating to the original cardholder's "member since" year that you refer to - but that is not the norm.
I'm sure folks with personal experience will chime in.