My new Amex Green reported today, and it IS indeed backdated!!! It shows the date opened as 05/1987!!!!! 
I pulled my new FICO scores, and was disappointed that I didn't see any jump on my EQ, and only a 3 point jump on my TU. But, I also allowed Amex to report my end of month balance, so my util went from 3% -> 6%. The old accounts that I payed off last month will report in about a week, and I'm paying off one more in a couple of weeks, so my util should adjust back down. I'll play with this -- at least that factor is under my short-term control.
I'm sooooooo happy!!! My AAoA got a 2 year boost on TU, and a year on EQ; this helps to mitigate the effect of all the new accounts I've opened within the last year. And, it anchors my overall history age at 24 years and growing from this point forward. I've actually managed to successfully add a card from a prime issuer WITHOUT taking a new credit ding, but getting a small boost instead!!!!!!
@Anonymous wrote:
Congrats! I'm hope I'm able to report the same soon. Again congrats!!
I hope the same for you, likewise. Good luck! 
@DI wrote:Hola, Tinuviel
Congrats on your successful update! Did AMEX report your new Green card to the CRAs after your statement closing date?
Hola, DI
Yes, it reported a few days after my closing date.
(o, en español ... Sí, se informó unos días después de la fecha de cierre.)
No soy latina; soy americana. Pero, he estudiado español en la escuela hace muchos años, y recuerdo un poco. 
What's confusing me, though, is that while it's showing up on EQ and TU, it hasn't appeared on EX yet. I have no idea why...