PIV: does it make sense to have a space under the door leading to the garage (non-insulated) but not to a closet under the stairs?

I have PIV (positive-pressure ventilation). The PIV installer told my contractor to cut a space (1cm or so) under each door so that the ventilation system could work. Makes sense, but:

- the contractor also did that for the door leading from the inside to the garage/bike-shed (non-insulated and unheated, though not terribly cold on account of being surrounded from all sides and from above by rooms or the co-op corridor; its outside door is a thick wooden door); this is then a weakness in the insulation;

- the door leading to the nook under the staircase was not cut in this way, and, perhaps because of this, that nook feels a bit musty (a bit of a concern since I'm storing the wine there).

Do both of these choices by the contractor make sense?