A patent date is when something was patented, not when it was actually made, many items were manufactured for many years after it the patent was granted.
The number for each year is the first design patent issued that year. Design patents refer to any new ornamental design for an item.
Patent and Trademark Office (USPTO) has a website where this information is available, and you can examine copies of documents that used to be available only in Washington or at a few large regional libraries.
Since some patents will have multiple classification numbers, you can widen your net by searching with these numbers.
You can also obtain classification numbers at "Tools to Help in Searching by Patent Classification" at step 3.
as you can with post-1975 patents, so that searching for patents by an inventor named Edison before 1976 will give you "0" hits.The United States patent number for each year is the first patent issued that calendar year.