Just hope you don't need to replace the spark plugs of any internal combustion engine-driven implement (like lawn mowers, weed cutters, or chain saws) that may be a few years old. You could be in for a rude surprise.
The model number found on your old plug type has likely changed--repeatedly--regardless of its age and manufacturer. That's when your replacement needs start to become a problem. The same type of plug may still be manufactured and even in stock at the store. However, trying to find the current replacement model-number is akin to finding the proverbial needle in the haystack. In addition, there are more manufacturers of such things now, each using their own and frequently changing numbering systems (an updated version will be available soon).