... As Angela says, JK&S stands for "John Kilner & Sons", which was in operation only between 1847 and 1857, so no[w] I know that 1961 is just a pattern number! ...
François — It's not that simple. You have to distinguish between formal company names, like those Angela listed, trading names, brand names and logos. A good name or abbreviation in any of these categories is a valuable corporate asset. Occasionally the main reason for buying a company is just such a name or logo. It is quite possible that "JK&S" was so well known and easily recognised within both the bottle making and drinks industries that it was never changed, whatever the formal name of the bottlemaker or its controlling corporation over the years. So I think the "1961" is still quite likely to be a date.
I love the Quebec Dairies website. Many of the links it provides are also well worth exploring. Here's the home page:
http://www.laiteriesduquebec.com
Bernard C. 8)