As far as we know, there is not a caliber 316L that exists, but that doesn’t meant that this number isn’t highly relevant to watches. In fact, 316L is a number that is widely used in the watch world.
This number represents a grade of stainless steel that is commonly used for watch cases and watch bracelets. You may also see watches made from 304L. Another grade of stainless steel is 904L, often associated with Rolex, which appears to use this particular grade more than other watch brands.