This is actually a good argument for never filling a tank with Nitrox unless it has the appropriate sticker. Non-Nitrox divers should always be able to tell they are getting air because they don't have the sticker.
Basing gas identification on tank stickers is something that has been refuted many years ago. Welcome to 2013. Even if you don't drink the DIR koolaid, you should know better than to base decisions like analyzing gas to a tank sticker. A sticker doesn't mean anything. Analyzing the gas yourself, and placing your own CURRENT marker (as way of a temporary sticker) is WAY much better.
The usual mistake of filling a regular tank with nitrox comes generally from places that bank EANx. It is actually more common than you would think to get this kind of mistake in such a setup. Having the wrong valves turned in the filling station, give you EANx in your non stickered tank. People SHOULD analyze their gas. They don't because at rec depths, anyhow, the danger is really minuscule (even with a slightly high PO2, you won't get in a really dangerous situation in terms of oxtox). The story is very different when you are going past the recreational limits, because then mixes can be become EASILY deadly because of either much higher concentrations of O2 in the mixes (50% deco gas, 100% deco gas, etc), as well as the potentially deeper PO2s you can achieve.
In the end, the truth is everybody should analyze their gas. The truth is in rec, we don't, and the stats are good enough nobody cares. Some even further the stats with the Nitrox stickers. But gas identification through permanent stickers, is NO NO. Assumption is the mother of all ****ups.
BTW all my tanks (4 80s, 3 40s) have NO nitrox sticker, no strange stickers, and get analyzed every dive. I use a couple of 80s as permanent 21m/70ft 50% tanks (with that MOD marked), 2 40s as 21m/70ft, and 1 40 as Oxygen 6m/20ft, and my backgas doubles who get all kind of mixes in them. I have a spare 80 that might get ... anything and has no markings.
