So the most basic question on this thread seems to be, how long will iodophor solution that has been made up retain its effectiveness if stored sealed up so that iodine won't evaporate (except into minimal head space?) Does it degrade by some process other than evaporation of the iodine?
The first thing to consider is that Iodine is naturally a gas, like other halogens such as Chlorine. Their natural tendency is to be a gas. Iodophor is made from an Iodine complex that creates a concentrated, liquid, soluble form of Iodine.
Basic usage info:
Always mix BTF Iodophor into cool or lukewarm water. The hotter the water, the faster the Iodine will gas into the atmosphere.
Mix rate: 1/2 ounce concentrate per 5 gallons of water; 1/4 ounce concentrate per 2.5 gallons of water; 1 tsp per 1.5 gallons of water.
Allow 2 minutes of contact time, drain, air dry. No rinsing is required.
Typically the Iodine mixed into solution will gas back into the atmosphere in roughly 12-24 hours, turning back to clear water. In a completely air tight container, this shelf life is likely far greater, but it's pretty difficult to put an exact number on it for time. There are things you can look for in solution color (amber vs. clear) and using Iodine test strips as a guide. Personally, I mix a fresh solution in a small batch every time I have a brewery-related task, then discard and mix new when I'm doing something again. It's cheap enough per use to do this.
Other things that will degrade the solution:
-Residual alkaline detergents. The Iodine complex and the Iodophor concentrate are acidic solutions. Mixing into any water that has residual alkaline detergent will neutralize the solution. I've run into people that have had issues running Iodophor through plate/counterflow chillers where there was residual alkaline detergent remaining in the system and it neutralizes the Iodophor solution.
-Excessive agitation or shaking
-UV light, so leave your solution in a dark place
As far as the concentrated product itself, National Chemicals suggests a two year shelf life for storage. However, we have run into situations where clients have turned in product over 10 years old and it passes QA tests. For best results, buy smaller containers and try to go through the bottles in about 2 years - or brew more!