From what I read, no one knows. I believe it is just that some years had different emblems than other years. I don't really think there were "extra special" crewcabs that got the unique emblems. Mine doesn't have any emblems, but it has been painted at least once.
1974 F-250 Crewcab Shortbed 4x4 460/4spd
1953 Ford F-100 Custom-- Current project --on Explorer Frame.
1965 Lincoln Continental Convertible Custom
2014 Lincoln MKZ Wife's
2016 Ford Focus -- Daughter's
2003 Lincoln LS --- Daughter's