Originally Posted by
Bearonabike
Correct. And if you read further, you can see this (with credit given to the BF member who runs that site) :
Originally Posted by
cudak888
The first of these two systems (noted below as "System 196X") started in the early 1960's - no earlier then 1961 - and ultimately rolled over to 7 digits sometime in 1970.
so your 995633 is a 6 digit 1970 serial number