In need of a Mopar history lesson

Just because one was a Dodge and the other was a Plymouth does not mean they were built at different assembly plants, both were Chrysler products. When I worked at Warren truck we built Dodge Ram Chargers and Plymouth Trail Dusters on the same lines along with all the Dodge Trucks. Before I retired in 2007 we were building the Dodge Ram 1500's, the Dodge Dakota's, and the Mitsubishi Raiders all on the same line. Yes the Mitsubishi Raiders had some different sheet metal but if you give them a good look they are only glorified Dodge Dakota's with the exact same drive trains.
Gotcha.

Lets take 1970 Hamtramck cars as one example.

Not many Dodge Darts but lots of Valiants including Dusters & lots of Plymouth & Dodge E-bodies too.

Two assembly lines, models all mixed up on the lines in actual production.

1970 LA plant, lots of Plymouth & Dodge B & E bodies for most of the year, all mixed up on one line. Then sometime in May of '70 all Es were built in Hamtramck & LA started to build As instead, but again mixed in with Bs.

Makes sense, now. Thanks guys!