Barry:
I think his question was whether there was a bulletin (or work instruction) that documents the procedure for painting the BB stripe. (To show that it was painted before the body). AFAIK, there is not such a document, but the engineering drawing is an excellent reference for the overall dimensions and placement (thanks again for helping me with that a couple years ago).
The masking explanation provided above is enough to convince me that the BB stripe was painted first. And I think the pictures of that green car (below) proved it also, right? (That picture is what I used as a guide to make the shape of mine look 'correct')
Anyway, when you paint your own car, the decision is up to you. I highly doubt that anyone will notice whether the stripe was painted before or after the car body. For mine, the only thing that made sense was to paint the car first, and then the stripe (opposite of the factory). That way, we could take our time and lay out the pinstriping tape, to 'eyeball' the look of the stripe. Then, we did not need to worry about how to protect the BB stripe while painting the car, or how to ensure that paint got between the large/small stripes properly.
-Tom