Many companies for many products list safe ranges for use based on trial and testing, but it doesn't mean they won't work outside those ranges. Sure, maybe don't use a yeast designed for low abv beers on an imperial stout but if your yeast is rated for 14% and it hits 17%, the yeast was just doing it's job in the environment that you provided. They won't quit just because they are like, WE HIT THE MAX LIMIT! They will finish when they are done. To a determent? Probably not.
Sent from my Pixel 3a using Tapatalk