I have 2 Chicago precancel stamps that appear to be a PSS #61 precancel. The question I have is are they the same precancel? The first stamp I am pretty sure is a #61 is a 1940 1c industry agriculture stamp. But I also have a 1966 5c George Washington that appears to be a #61 also. Can cancels or devices be consistent 2 1/2 decades later?