Just looking at the picture, my first thought is that is a much later added stamping that may have been used by some state inspection authority to verify/certify the original data plate, maybe if there was an issue with an error on a title.

My thinking is the "SCC" would indicate whatever jurisdiction did the inspection, the "56" confirming the plate/vehicle year and the "1 97" may indicate the month (January) and year (1997) when it was inspected/confirmed.

Any history on the truck beyond your currently provided info (I peeked at your other posts)???

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)