Thanks, one of the posts in that thread refers to logging into his Everyday Amex and doing the offer from there and getting the bonus.
I just did the same and it shows offers for Gold and Platinum but if you click the terms and conditions, they both clearly say "not available" to applicants who've had those cards.
The offer codes I see for the Terms and Conditions document are:
POID BRLT:0005 for the Gold card.
POID CF6S:0002 for the Platinum Amex.
So it would be good to see if people post offer codes for those without the Welcome offer "not available" language.