Well, in the era many lines used the Miller Coupler for passenger cars. The Carson & Colorado and SP for a while. I've seen pictures of Millers on the Rio Grande. And then we can go counting all of the standard gauge lines that once used Miller couplers.
What is unique about the Boston, Revere Beach & Lynn is that it continued to use Millers much later than anyone else. Probably this was because it was intrastate commute operation and not part of the interstate system.
The B,RB&L used Millers and vacuum brakes until it converted to electric operation in 1928. Then it continued with the Miller couplers on the electrified passenger cars until the line shut down January 27, 1940. There is a photo published in a history of the line clearly showing the Miller coupler on the final fun.
Brian Norden