there is no real standard of measurement. its really what the maker determines and labels. if a barrel maker has pretty good barrels and then sells match grade it generally means the barrel rifling and bore diameter crowning etc are more uniform.
just because a barrel has been air gauged doesnt mean they arent tossing em all in the same bin regardless of results...
match grade can often be a marketing term rather than a useful designation the buyer can use. i would be more willing to believe a match grade air gauged barrel from the colt custom shop is a better barrel than the standard one than i would be willing to believe it of taurus as an example.
an air gauge pushes a measuring device down a bore to determine uniformity of rifling
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith