Mine are getting gently bleached as I type this and are unvailable for photographs. I have just checked and the eBay pics show a folded shirt, so you can't gauge much from them. The bib is just like the bib on any other boiled/ formal/ pique / marcella front shirt, except there is no fly.

There is a style of ladies cardigan sweater that some clever girl figured out could be worn buttoned up the front or the back. This is the theory behind a button-up-the-back shirt. If a shirt is a tube, the closure of the tube can be anywhere you want it to be. Most of the time, the front makes the most sense. But for the formal bib front shirt, the studs are purely ornamental. As many people have figured out, manipulating the little spring mechanism on some shirt studs through two layers of stiff, but moving fabric can be tricky. Here is the genius of the single bib, as explained by MoR above. As he also pointed out, there is no risk of Gap-Osis. Nobody will know if you are an AC or a Champion guy, or whatever company sponsors your tee shirt.

I don't think anyone dreamed of removing one's jacket while wearing such a shirt.