Kevin!
On my car I have found parts from April 1964 to week 5 of 1965. There might several reasons;
1. The supplier shipped the parts with a regularity that Chrysler required without any problem. These parts have a short time supply which means date codes are close to assembly date.
2. Same scenario as above but the supplier had problems. The time for storage at the plant is longer which means older parts for the assembly line.
3. The supplier had huge problems with just-in-time shipments which required shipments from other plants. I know that the LA plant had most of the parts produced by suppliers in the neighbourhood.
4. I've heard rumors about some supplier that had huge problems with delivery due to some unknown problems. That caused the scenario that the plants were pulling cars off the line until the required parts showed up!!
On my car the most common date codes are August to October of 1964. That is simply the reason for choosing August 22 as date code. Since my friend Johan had his trunk mat with that code it is easier to have something to compare with so the fonts and style is the same when I did the stamps.