Just out of interest, how are you harvesting? (top or bottom cropping)? and what striains do you use?
I have Whitelabs 002 English, 013 London, 022 Essex and Wyeast 1469 West Yorkshire. The Essex yeast I bought around March 2018 and have brewed 14 beers with it and have one fermenting at the moment but the starter was sluggish, normally goes like a train, is although I have harvested this brew I might call it a day with this one. Also got a feeling I only have a couple of brews with the Yorkshire left. I top crop the yeast head and also a small amount of the wort at the same time to store it under.