National Guard ASNs issued under Selective Service will inevitably start with 20.The third digit will be the CORPS AREA.These are 8-digit numbers.
Pre-Selective Service numbers are 7-digit and start in the 60s and up through the 70s---such as 6522723. A guy who was "in" prior to Selective Service did not necessarilly get a new number.Sometimes they did....each case is unique.
The "6x" seven digit numbers are SEQUENTIAL and I have never been able to derive location or time data from them.
Dave Berry www.pathfinderhistoricalconsultants.com