At this year's national meet, the subject of trim tags came up. The chief judge stated that unpainted trim and body tags are acceptable for judging. Originally, however, tags on all cars except for the Darrins would have been painted since they were attached prior to painting.
If your car has "bare" tags, it's probably because the paint fell off over the year. Both of my 47's and my 50K all have tags with paint on them, however, the tags on my 53 and 54 only have traces of their original paint yet the later cars are in much better overall condition. Go figure...