They are, but the first three numbers indicate which state they were issued in. After '72 it has been based on the ZIP code in the mailing address provided on the application for the original Social Security card. .
From the SS Administration itself
575-576 indicate a card issued in or to Hawaii.
Thanx
The next two numbers indicate the time period. (My sister & I were born in 1970 & 1972 and the first 5 numbers of our SSNs are identical.)
It always bothers me that people give out the "last 4 numbers" of the SSNs not realizing those are the only real unique identifying numbers in their SSN.