Actually, they all should be labeled, the missing label just means it fell off. 
It's possible to identify the -08 and later ones from the -07 and earlier ones without the label, but I don't know of any way to identify a -08 from the -11 or -13 versions. The -7 had a reversed polarity on the marker and light outputs, and anything earlier than the -7 has a tunable can and not the black ceramic resonator.
