Non standard,
I can see what your National bee inspector is suggesting, but might the extra super be better fitted under the crownboard and avoid the roof ventilators being propolised? They certainly do that, as I experienced it in my early seasons, which can, in turn, lead to damp and mould in the roof space). Not the sort of advice to be passed on to a lot of new beeks.
My main point being that if he either wants to be a lazy beekeeper or just does not have any idea of the space required for storage before the next inspection (the only real advantages) there is no getting away from the heating of that extra super - potentially a big problem this summer.
Further,what he might refer to as summer (not seen much of summer weather yet) and it is counter to the vast array of beekeeping books over a very long period. Every one of those refers to the crownboard as the upper limit of the bees' access. Full stop.
It is plain common sense to avoid comb in the roofspace, so frankly I view this sort of gimmick as an excuse for not attending to the needs of the colony. Might just as well add two supers and be done with it.
The next question that seems obvious from this and follows any line of common sense is why doesn't he avoid the probability of getting roof vents propolised by adding a real crownboard or one with with gauze fitted (so the bees propolise that - because they will)?
But overall, you are still, by admitting the vents will and/or do get propolised by the bees, still means that gaping holes are not the order of the day.
Back to thread title. Feed holes are not ventilation holes, I never seen a book which refers to feed holes as 'ventilation holes'. And to be honest, I don't think I have ever seen a book referring to any other gapong hole in the crownboard for ventilation, either.
Lets get real here, whatever you do, if the bees can put it right, they will. They will tell you it was wrong by their actions. But only if the beek actually watches, observes and understands their (the bees) actions. Otherwise you might just as well do the proverbial in the direction opposite to that of the wind.