I’ll been crunching some production numbers and for thoughs of you that may find it interesting, I’ve put together a spreadsheet of Firebird's rolling off the assembly line. The Build/Month data is published data but the cars per day from the plant is an estimate. It's interesting the 84 model year was so long. They must have been getting ready for the 85 model year changes; there were a lot of changes.

It also looks like model year changeovers spilled over into the first day of the following month so I speculate the VIN was generated the previous month and it took the factory an extra day to finish producing those vehicles