Other cars from Baltimore have had the paint code on the tag.
Here's a special paint Carousel Red 69 GTO convertible - and although carousel red was the standard color for Judges in 69 it was an extra cost solid special code for non Judges. Code on the tag is code 72 rather than --.
If the code was in the system, I believe it went on the tag - if it was not, it got the dashes.