I am not trying to be a #&%@ about your claim, just stating some facts.
True, someone with a lot of knowledge and history of Chryslers vehicles has stated that his records show that your car is a very late build, and is the last one that his records show as being built.....So far! What if tomorrow someone send him a build sheet that is one number later than yours?
That said, the build date is not necessarily the actual date the car rolled off the assembly line. So even though your car could have been the last one across the line, it would be very difficult to prove unless Chrysler kept those records, which they didn't or you or he where there to witness it.
It is cool that your car has a late build date, but even if you could prove that your car was the last 71 ever built I don't think it makes your car that much more valuable than any other 71 with the same options.