OK, kids, the "D"-body applied to the '64-'66 Imperials only! After that, they were considered "C"-body cars from '67 to the end of Imperial production.
The "Y" is the car line!!! Example - A 1967 Coronet is a "B"-body, but the first character of the VIN starts with a "W". You never hear of one referred to as a "W"-body, do you? An Imperial VIN starts with a "Y", and is NOT a "Y" body car.
The only Imperial to actually BE a "Y"-body was the '89-'92 front-wheel-drive Imperials. The Factory Service Manual validates this.