A big thank you to FlyGuy! What follows is proof the methods he posted to freeze yeast works:
I took a new vial of White Labs Kolsch yeast, WLP029 with an original best-by date of 7/3/2012 and froze it on 4/6/2012, storing it inside a small cooler with ice packs inside a top freezer/fridge. I moved 2000 miles across the country in the fall of 2012 with this, and other yeast strains, packed in dry ice. In February 2013 my fridge broke and it was only the small cooler with ice packs that protected the yeast for about 8 hours before I was able to transfer it to a working fridge. My point is; this yeast has been subject to variations in temperature.
I used 16ml vials and filled them with 7ml of settled yeast, then added 6ml of 50/50 water/glycerin. This left 3ml of head space in each vial, and by my calculation is 23% glycerol. I used Walmart USP glycerin from the cosmetics aisle, and meticulous sterile technique with a pressure cooker, etc described in this thread, at home.
In early-July 2013 I removed a vial of this Kolsch yeast from the fridge and stepped it up a number of times. I started with a 150ml 1.020 starter, the 250, 500 and 1L starters at 1.040. In between each starter I put the yeast into the fridge to settle, then decanted the spent wort and added more each time. My starters were done on a stir plate.
Last week I took the final settled yeast and stepped it up again using a 1.5L starter at 1.040. Then on brew day I made a 500ml starter and pitched the entire starter into my 7.5 gallon batch of wort after about 12 hours on the stir plate. The OG from my refractometer was 1.054 and tonight after 6 days of fermenting I took a sample and it was at my FG target of 1.009. The beer tastes good too, albeit flat.
In short, I can say that 7ml of Kolsch yeast frozen for 15 months in a regular consumer fridge with 23% glycerol solution was successfully used to brew a 7.5 gallon batch of beer. Tonight I'm taking a vial of Denny's Favorite 50 (Wyeast 1450), that was frozen in 4/2012, and will attempt to bring it back to life too. I'll post my results with the 1450 when my next batch of beer has fermented out.
Thanks again FlyGuy!