The surprising thing was how certain the tailor was about these facts. He told me that double-vented jackets have been out of style "for at least 10-15 years."
There is an argument to be made to the effect that he is correct. In fact, I generally tend to agree with him. Just because forum group think dictates that 1/2" of sleeve should show doesn't make it an immutable Law of Eternal Style. However, vents and the amount (if any) of shirt sleeve that shows are both entirely a matter of personal taste.