Need Sequence Number Education

I plugged the VINs for a couple of cars I have into the VIN Decoder & these are the two sequence numbers I got;

724890

726360

These have something to do with the 10,000 day calendar, right? How do I determine the build dates from these? I looked in the tech archives & couldn't find the answer, but I might have missed it. Both cars are 1964 Barracudas.