AMEX refer a friend bonus – when does the clock reset

[WorldFlyer]

When is it possible to receive refer a friend bonus MR / AVIOS, etc again, once maximized on a card? It is after having the card for 1 year or after the new fee kicks in or when is it?
I have the Platinum card, however, maximised the 90000 MR earlier, after they had the generous 24000 MR bonus points for a friend referral.

[Reney]

1 Jan.

[WorldFlyer]

Thank you, I would have thought it was per card year, thank you for clarifying it is per calendar year!