It’s important to remember that at the moment this change is only effecting new accounts that are opened, if your American Express card has already reported the old date then it will continue to do so.
This also won’t affect the member since date which is shown on the front of your card, only the date reported to consumer reporting agencies.
There are a number of theories on why American Express made this change (something to do with trying to keep Costco cardholders – which makes little to no sense to me).
The most likely reason is that they were either receiving pressure from regulators, consumer reporting agencies or even other financial institutions.
Although in exceptional cases – where third party rights are not affected – the courts might be persuaded to treat the stated date as being the effective date, a situation we return to below. There are rare occasions when it may be permissible or even justified to do so.However, at common law this was a criminal offence (going by the contradictory sounding name of uttering a false document) and in most English law based legal systems it is still an offence today, although in many cases statutory provisions have superseded the common law (for example, in the British Virgin Islands see section 242 of the Criminal Code 1997).Where backdating is done for financial gain, it may also constitute the more dull-sounding criminal offence of obtaining a pecuniary advantage by deception.Parties seeking to enforce rights can find those rights barred by ancient common law doctrines like (“from a dishonourable cause an action does not arise”).In certain cases a criminal act may negate insurance.