Wanted to bring this topic up again because i came across a suit the the other day that is from Banana Republic. It is advertised as a two button suit, but if you look closely in the photo above the top button, it is actually a 3 button that was "converted"LINK to site
They sell it as: Tailored grey tweed two-button suit blazer
Saw it in the store as well and it is interesting what they have done. Creates a interesting little tweak to the suit.
Also in the image they show the button hole as being stitched in grey to match the suit. But in reality it is a darker grey/black that makes it stand out much more than it does in the photo.
The whole thing makes me think it was a massive manufacturing mistake. Made a whole bunch of two button suites, but put a third button in, and then, oops.