[exray]

We'll probably never know the chicken-and-egg arrangement between Clinton and Plant A. Some Clinton branded sets actually have a Clinton chassis tag. Coincidentally its the same orange color and style as the more common Plant A tag There is also service data out there for their larger 10-11-12 sets but not for the smaller ones.
I suspect Clinton made their own large sets and farmed out the smaller ones to Plant A. However, at the end of the day, they could have all been made under the same roof!