I would be AR'ing every other boiler if this applied to room sealed.It is still at your discretion. I resat mine 2 years ago and I spoke to the gas safe bloke about it as my thing was no terminal guard and flue hole not sealed so how can I AR that and thats when he said about your discretion.
The discretionary multi NCS elevated to AR applies to open flue only as a number of flue & vent NCS's may amount to something more dangerous.
If I am incorrect I really need to back to basics.