Ok, a couple of things.
Bakers use the same yeast again and again for years and so do brewers. Keeping it cool will put it into a dormant state; however: Bacteria and yeast reproduce about about the same rate, so if great care is not taken with hygiene etc., then you can lose your 'personal' yeast. So the main issue is contamination and one thing bakers and brewers will do, is to only use a part of the 'stored yeast' for their next batch. Once said batch has been completed and approved, a part can be added to the 'store'. In the old days, they use to have a wooden box, called a grain or flour store. The lid was used to make the bread and that was also where they kept a little of the last mix, made. However: They made bread every single day and so offered little time for things ot go bad.
I make Rum and have a number of what are know as 'Rum pits'. They are not actual pits, just the yeast etc. stored for my next fermentation batches. I always try to keep two from the same batch, but stored apart from each other in case one goes bad in any way. I have different batches for making different kinds of rums. If I am making the next batch very soon, then I just keep them in a cool place, but in the winter; when I don't make any, I store it in the freezer. This works find for me, the boss is not too impressed with half a dozen paint pots, stored in the freezer though.
