Yes, but today - even if it isn't "PC" some of us generally refer to the 51s and 52s as Bonus Built as well (and it's generally understood) because the 51s and 52s were catagorized with the 48-50s because of the very similar body style and design characteristics. I call my 51 a Bonus Built mainly just to differentiate it from the Effies!

I guess it's like calling a Fuscia Sweater Pink.

And everyones right, it was an adveritsing nickname to compete with Chevrolet and the51/52 years focused mainly on trade in value and operating economy.