@benbradford I've read and reread Chris White and Jamil Zainasheff's book Yeast several times since it was first available and also have successfully rinsed/washed yeast for future batches for even longer than that. For me storing the washed yeast at 37F and making fresh starters before using it to make beer is all that is needed.
If you have stored yeast for three months or more it makes sense to make a starter, ferment a batch of 5% alcohol beer and then repeat the washing process. The resulting second generation of your very own 'house yeast' can then be safely stored for several more months. At that point you can decide to toss out any remaining vials of first generation yeast you stored previously, or hold on to it longer.
If you have stored yeast for three months or more it makes sense to make a starter, ferment a batch of 5% alcohol beer and then repeat the washing process. The resulting second generation of your very own 'house yeast' can then be safely stored for several more months. At that point you can decide to toss out any remaining vials of first generation yeast you stored previously, or hold on to it longer.