The US census documentation for state codes is missing several numbers. For example, there is no state with code "03", "07" and others.
Here is the start of the list...
STATE|STUSAB|STATE_NAME|STATENS
01|AL|Alabama|01779775
02|AK|Alaska|01785533
04|AZ|Arizona|01779777
05|AR|Arkansas|00068085
06|CA|California|01779778
08|CO|Colorado|01779779
09|CT|Connecticut|01779780
10|DE|Delaware|01779781
...
What exactly happened here? It's not as though there are constantly new states joining and old states leaving. This list should be pretty stable and predictable.