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.