I think that today FAA & EASA accept products in commercial aircraft that are not compliant with FAR25 (for example FAR25.853 for flammability) if they are compliant when they are tested "in sandwich".
you have product A which is compliant to FAR25.853
you have product B which is NOT compliant to FAR25.853 alone
but product A with product B are compliant to FAR25.853, so both (A and B) products installed in the plane are allowed
It seems that this rule is going to change and to be stricter. Each component will need to be compliant to FAR25.853 when the product is tested alone.
Does someone know if it is already the case or when it's going to be set up?