This is the rationale that I have used in trying to estimate the build date of my Norwood 01C built '69 RS. As a start, I referred to the VIN # production by month info on CRG site at: http://www.camaros.org/geninfo.shtml#When
For example, let's look at Jan 1969 Norwood numbers.
First unit produced in Jan '69 VIN: 569987; Last unit produced in Jan '69 VIN: 589720; Total units produced in Norwood in Jan '69: 19733
From the following link: http://www.camaros.org/forum/index.php?topic=983.msg5279#msg5279
JohnZ tells us that Norwood produced 912 units / day. In January, there are 22 "production days" (assume Monday - Friday and excluding New Years day = 22 production days in Jan '69). 19733 units / 912 units per day = 21.64 production days or rounded up = 22 production days - so far so good.
My car is VIN #581767, or the 11,780 unit built at Norwood in Jan '69. 11780/912 = 12.92 days. Starting with Jan 2 as day 1, and excluding weekends, the 12th day of production was 17 Jan (Friday) and the 13th day of production would have been Monday, 20 January. Consequently, I would conclude that most probably my car went through final assembly at Norwood either very late in the day on Friday, 17 Jan or very early on Monday, 20 January 1969.
Another reference point is the date code on the Powerglide transmission in the car which is the original transmission. Obviously, it had to be buit prior to the final assembly date of the car. The date code on the tranny is: C9A16N, which decodes as being built in Cleveland on Jan 16, 1969 during the night shift. Not impossible for the transmission to have been shipped from Cleveland to Norwood for final assembly on 17 Jan, but final assembly on 20 Jan is a better fit. No way to know for sure, but that's my story and I'm sticking to it.