Interest free period on Personal Platinum Charge Card – Max 56 days or 42?

I have a Personal Platinum Charge which I’ve had for a few years but also a Business Platinum Charge (since the past few months) as well as Platinum Credit (previously a Gold Credit and upgraded to Platinum on the recent offer).

The max intrest free period on the Business Platinum Charge and Personal Platinum Credit is 56 days (payment is due 4 weeks after statement closes) but the Personal Platinum Charge has a max interest free period of 42 days (payment is due 2 weeks after statement closes).

Shouldn’t they all be a maximum of 56 days? I don’t have a direct debit set up on any of them but did some years ago on the Personal Platinum Charge which I stopped so maybe this is why?

I queried this with my Amex Business Account manager who said it was correct but I’m not so sure?