well according to you the "Mylar sticker" is the actual build date. But the correct name for it is a Compliance Decal, If you carefully read what is printed on the Compliance Decal it is self explanatory. read what it says not what you think it says.
"This vehicle conforms to all applicable U.S. FEDERAL MOTOR VEHICLE SAFTEY STANARDS IN EFFECT ON THE DATE OF MANUFACTURE SHOWN ABOVE", meaning it was built in compliance with the regulations that were in effect or use at the date shown above.
In my "opinion" on what I read or have read upto this point leads me to believe that there is no actual way to verify the actual finish date of the vehicle. Therefore in my "opinion" the only factual date basis for the production is the "spd" as you call it. The production of the was started on a certain date when the order was taken or scheduled by Chrysler, the order taken ,broadcast sheet filled out, fender tag made, order placed in line and then what ever happens next assembled or delayed for what ever reason. That is my "opinion" so far and is exactly why I asked the Questions I asked. as for the "Compliance Decal" it was most likely the last ID. placed on the vehicle however the date listed on the decal was merely a confirmation of standards in effect at that time.
With all of that information and the fact that I stumbled across 3 vehicles roughly built in same time period ,has T/A block unstamped, and all have the same casting date block, some shortly before "spd" and some after "spd". enough of a coincidence for me to ask Questions, not mention the Welborne - Andlucci thing. So the answer to your question do I think it is possible yes I do think it is possible, but not for certain one way or the other until I find out if there are more cars with the same scenario's . Do you really stand by your statement that the "Mylar Sticker" is the actual finish date