Well think about it.
When you find that Buildsheet,it's found in the Car itself,put there by the Assembly line worker.So there is No way the Carriers signature would show up on that particular copy because it's still deep inside the car upon shipment/delivery.
Now notice the number 2 surrounded by the larger C made of X's in the lower right hand corner.
That shows there was more then one of these sheets,and the car had copy #2 in it.
I would suspect that one of the other numbered copies would show a signature,as I have a few Buildsheets that actual have the number 4 & 7 down in the Lower right hand corner,found deep inside some cars.
So many copies were sent all over during final assembly.I would imagine one of those would have shown a signature,if they are still around at all.
*I've always wondered if instead of asking Chevrolet for copies of the Cars buildsheets,if we asked the various Trucking Companies who shipped these to the Dealerships back then,if they would still have their 36 + year old records..