Ok no one has seen that writing on the inside before??? Why would someone take the time to write the September 1968 date? Could this be the first one of that color produced? Maybe this is something to look for in the early 69 cars? The 1st is maybe the 1st shift or first run? B/SS/37 = Base /Super Sport/ 3 7 = Z28 (style trim and not) this is quite the curiosity, even if the guy decided to eat his lunch in that car and thought "hmm let me make write that his is the first green one Im doin" Maybe there is the the 1st blue and first red etc out there. Is this a Los or Nor car?
Lots of maybes there. It looks nothing like the known markings from the assembly lines, where cars were rolling down the line and markings were a quick scrawl with a crayon or a paint marking. IMHO it's too new in appearance, too long and wrong format, and was not a factory marking. I highly doubt someone in an assembly line would go to the trouble to write 1969CHEV when it was already obvious.