I can't say as I don't use air-tites, I do use the intercept and know when the inserts change to a brown color they have out lived their corrosion inhibiting properties and it's time to replace them. I use them on better copper coins to lessen the chance of moisture and corrosion on the surfaces now that I'm in a more humid environment (a far cry from Denver's dry arid air). I also keep desiccant packs with them and store them inside air tight Tupperware type containers, which are checked on regularly. I don't worry anywhere near as much on silver or gold coins.
"Buy the Book Before You Buy the Coin" - Aaron R. Feldman - "And read it" - Me 2013! ANA
Life Member #3288 in good standing since 1982, EAC Member #6202, NBS Member, 2¢ variety collector.
See my want page: http://goccf.com/t/140440