The 1977 I bought last year (my first Corvette) was built with option code 7D001XA / SPECIAL PAINT - BODY IN PRIME.  According to the Corvette Black Book, only 80 1977's (out of 49,213) were built with non-standard paint or primer only.  The previouis owner was unaware of the rarity; I didn't know anything about it either until I got a copy of the original dealer invoice.  I have been unable to get a total for the primer only cars.  Does anyone have that figure documented?  Also, I've heard the primer only cars were shipped to dealers with all emblems, etc. in place so things had to be removed for the car to be painted.  Is this true - in case I ever wanted to restore mine to "original." 

It is impossible to document the exact number of "primer only" cars from the factory. There have been no records found for most of the mid-70s cars to prove or disprove much.
It is true that the primer cars were delivered with all emblems/trim installed; this is true of any year model.
In NCRS judging, if the car is documented as being delivered in primer, then the car has to be shown in grey primer in order to gain any paint points. The primer cars would have had a special silver/metallic flex-paint on the front and rear bumper covers, not the normal grey primer.
Plant info on the mid/late 70s Sharks is slowly turning up, a little at a time. One of these days, there will be much more positive proof of how stuff was done.