I tend to follow the BPG and presumably showing that you have followed that would also be a way of covering yourself if something happened - given that terminal damage should always be a C2 (and any loose terminals fixed at the time), and that is the most likely cause of a consumer unit fire...
Having said that I do usually C3 a CU if it's on the escape route or under a wooden staircase - and sometimes add a recommendation that no combustible materials are stored near it.
I agree that there is a subtle difference between ticking the box and the BPG saying 'no code' - they aren't quite the same thing...
However, I also tend to add comments to my certificates to cover things like that there.... with no code, but COMMENT in the Code box. It can also be covered in the comments on condition of installation too.
Though also quite a few of the installations I've inspected are old enough to pass because they are pre-plastic, so it's clearly going to be decades most likely before plastic boards are a rarity, either way...