As the nitrate content of gunpowder is a strong oxidizer there was never a need for air to aid combustion. The vent was necessary in a flint lock to provide ignition but after the initial ignition no Air was "Drawn In" but rather there was a "Blowing Out" of gases which lowered, not increased, the ballistics of the arm. With guns now having been ignited by percussion for some 200 years I think the "Need" for a vent has been thoroughly De-Bunked. My Isaac Hollis percussion double has no vents or plugs of any type, nor are any needed.
as for flinters - true enough - learned quickly if you stood in the firing line with some one who enlarged a "touch hole" to improve ignition - and the reason as reentactors we we required to have a vent guard on the lock to make shoulder to shoulder in a volley safe
and although we may now know they are not needed in percussion guns, the concerns of the age - or at least the marketing of the age - saw them as a better grade feature - i have always heard them called "blow out" plugs - and when unvented - i can see no other (valid or not) reason for them
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