I found this interesting explanation on the Transamcuda.com site. I'm sure that although this was for the 1970 MY it applies to many years before and after. So if your MoPar has "quirks and/or anomalies", this from an authority who was there should shed some light on your car especially if it's somewhat original. Copy and pasted: There was a post recently about which exhaust manifold was correct for AAR's and T/A's. Years ago when I first started my site I posted what I thought at that time was the correct ones. I received this email from Bruce Thomas. As you will read you see his explanation on this. This was sent to me mid to late 90's. At that time he owned an outstanding AAR Cuda. Here was his email to me. Jeff, I was asking about the exhaust manifold. I have seen a good number of AARs and TAs both "original and restored" which had exhaust manifolds with and without embossed part numbers. I have worked for Chrysler since December of 1970. At our plants we only identified and tracked parts by the Chrysler P# (Part number). Date codes had no bearing to our line workers. If the part number was correct the part was used (sometimes it did not have to be the correct part number. It just had to fit. i.e. one white door panel and one black door panel or a Dodge emblem on one side of the car and a Plymouth on the other side). When the lines were filled with parts the assembly workers would use the correct part number that was most convenient / closest to them. Many times that resulted in the older stock staying in the back and the newer stock being applied. Every so often the line Supervisor would have the work areas cleaned up and the stock would get shuffled. Stock that carried a Supplier Date Code of last year would be used the next year if the part was "interchangeable" (different Part number but would also fit) or used if it was a "carry over Part number (i.e. a part number for a 1969 unit was also used in the 1970 model year.) In short, as long as the part was at the plant and would fit on the car it would / could be used. Once we got to the end of a model year ( This was called "Build out"). We would build all remaining cars in our "Build Program" using whatever parts that were there. Sometimes a car would get built even if all the needed parts were not there. These build out specials would sometimes look very strange but the Plant manager made his production quota. Even if it did not have all 4 wheels. Of course these cars were not supposed to be shipped to our Sales Bank until they were corrected.