Is there any way to precisely determine when these vehicles were built? I highly doubt it. Naturally, Chrysler Heritage only has records going back to 1930. Just as well, with them in bankruptcy, the janitor is probably running that department and I'd never see that money again!
Using the chart Chet posted, I took my Fedco number, date, numeric sequence, etc. and determined my '29 was built on or around 11 June 1929 (80th birthday coming up!). I also found that the 100,000th Plymouth built was manufactured less than a thousand cars before mine; just a few days, which I think is pretty cool. What would be very cool is if it mine actually was THE 100,000th Plymouth.
Anyway, if someone is an automotive archivist that specializes in pre-depression era Chrysler products that has a magical chart, lemme know!