As with fender tags, each plant did things differently.
Big picture....different parts of the plant assembled different assemblies of a car. Each station received a broadcast sheet for their specific assembly, hence the term "broadcast". The "C" indicates the trim shop where the sheet for a specific car was inserted in the front and back seat cushions for a specific car.
The sequence number is, probably, unique to the sheet. The scheduled production date is part of the shipping order number.
What the actual numbers mean varies by plant. Recent research indicates that, for some years, the number is related to the actual construction date at the St. Louis plant. At the Hamtramck plant, the numbers appear to be related to actual plant construction sequence. Different plants had different protocols for the sheets during assembly. The LA plant left few sheets in cars so finding a sheet from an LA built car is not common and a great find. Hamtramck seems to have left a lot of sheets in the car. I'm not familiar with how Jefferson, Windsor, Belvedere and Newark plants handled sheets.
What the numbers mean could probably be determined IF people would save, collect, and analyze C body info from the different plants. Hint....hint.
