So about the only way you could get a set of multi colored stamps was if 1 or more of the inspectors was happy and put their stamp on, and the 2nd or 3rd rejected the car for his area. Then the car had to be repaired for whatever caused it to be rejected and then got reinspected on another shift. Say the Paint and Body inspections went well and got orang stamps, but a peice of trim was messed up, or incorrectly installed and got rejected. The car got pulled aside and someone would have to come and fix whatever the issue was before the "T" guy could affix his stamp. If the car was originally inspected near the end of a shift, it could be the next shift before the issue was resolved and the car reinspected and stuck back onto the line. So now you end up with orange P, and B's, but a green T on your firewall.
I'm assuming they had to pull it off line at the final inspection point if it failed to get the issue resolved because there would probably be very little time to fix it between the inspection, and the body going thru the wall the Chevrolet.