@WOLFGANG
My car's year of manufacture, regardless of what it says on the CMC plate, is 2001 because THAT is the year I completed the entire car and got it on the road - That's documented by Mass. registration records. The CMC plate is only for a component of the entire car (the body). Not only were they not interested in the CMC YOM plate, they didn't even wish to see it! All they cared about was the sales invoice showing the sales date and that the body was not stolen and was legit.
I later added the CMC plate to the door jamb just to make it look like a coachbuilder made the car (yeah, ME!) (Actually, I got tired of it sitting on my desk for 20 years).
Because I could prove that the engine was built before 2007 ( I had the invoices for 1997 ), I am emissions test exempt.
I cannot use YOM plates for a 1969 car any longer, because the title/registration says it is now a 1957 car, so I could use a single, green-on-white, butt-turr'ble Mass. '57 plate on the rear only, or an "antique" plate but those restrict how much and when you can drive the car (to/from shows and on weekends under mileage XX) I could do a vanity plate, but the ancestral "Sumner" side of the family and "Cheap Yankee" in me won't let me shell out the vanity bucks (and besides, some lady in Roslindale already has the "Pearl" plate - We checked).
BTW, all of this titling and registration stuff sounds very involved and mysterious, but let me tell you, it is not. All 50 states and most territories (not sure about ALL of the territories just yet) can share title and registration info instantly between states and offices - including boats in many states. IIRC, aircraft are handled in a different database, but the info is shared the same. When I visited the Mass Title offices I had a complete title history from the initial delivery from the boat to the first dealer through subsequent owners in three states up to my purchase and my three state moves, in my hand in less than a minute after I asked for it. Even Florida and South Carolina can do that, if they want to (some states do not share this info with the public).