Commercial vanity plates first appeared on the blue base, possibly in 1979.

These "pairs" were seen on eBay ... standard (passenger) vanities on the 1977 base, and then the identical commercial vanities
on the blue base, stickered all the way up to 1992.

Were the tan vanity plates on commercial vehicles ? Maybe.

1977 BASE

1979 BASE

1977 BASE

1979 BASE

Evolution (more like degradation...) of a commercial vanity plate.Jeff Fazekas

2001

2004

2009

Here is an interesting combination.
The TNT TR5 commercial vanity plate was on a landscaping truck, and
the TNT-65S (a regular-issue trailer plate) was on the trailer it was pulling !

Nice coincidence ... or somebody knows somebody ;-)
Pictures from Jon Cohen

All of the OTS plates come from On The Spot Home Improvements, a local business.
There are others (up to -12) on the embossed base shown above.