What are the requirements for the Marriage Certificate when travelling to UK with an Article 10 Residence Card?

I'm a British citizen and my wife is from the Philippines. We live in Spain and she has an Article 10 residence card with 'Family Member of an EU Citizen'. We'd like to visit the UK in July and she should be able to enter visa-free with her residence card as she'll be travelling with me.

The Gov.uk advice page says that we'll need to bring our marriage certificate as evidence of her right of admission. Our marriage certificate is from the Philippines (in English) and has been authenticated by the Department of Foreign Affairs in Philippines and legalized by the Spanish consulate in Manila. It's dated in August last year.

I haven't been able to find any information about any requirements for the marriage certificate. We had trouble getting the Spanish government to recognise our marriage certificate when applying for my wife's entry visa + residence card (lots of crazy requirements like it not being allowed to be more than three months old) so I'm worried that UK border control will try to impose similar requirements when trying to enter visa-free.

Does anyone have any experience or knowledge of this? Is it possible that border control won't accept a foreign marriage certificate as evidence and won't allow my wife to enter visa-free?