I bought this billboard 71 Hemicuda in 1986 in upstate NY, from the owner who bought it new on the dealership lot the next town over.
I visited the dealership several times in the 80's and they remembered the car well.
Talked to the selling salesman, showed him this picture ( original untouched paint, 33,000 miles in photo ) and he stated it was just as he remembered coming off the transport.... 'big ugly stripe and all' as he called it.
I'm with Mike on this one ( the Mike who states they were initially installed at the factory ).
I tend to believe more were installed at assembly than not.
This is a December 1970 built Hemicuda.
I also have a 71 340 billboard Cuda that I bought in 1976 from original owner who told me he he was called to the dealership the day it arrived and it had the billboard on, just the way he ordered it.
Anyone who has ever installed this stripe knows it is no treat doing so.
I could see a dealership employee having a fit trying to figure where to cut and overlap the stripe on the quarter panel unless instructions were sent explaining that.

hemicuda7.jpg