How often is that seen? IMHO not often
Looking through my collection all were painted (on those that had what appeared to be original paint and included a clear picture of those items
Now its possible (would need to compare the point in time of the unpainted ones found) that unpainted was the norm for a specific period of time.
Armond - yours is a March 13th car car below March 15th. Really close to one another so I'm at a lost of why the difference in production practice in this example being so close to one another. Second picture below is from a car with a VIN before your car (1876 numbers before - sorry no Marti or real build date)
Here is a shot of or original paint trunk bolts from the one I own.
Second example