Hmm! That is interesting!

The difference is the position of the "Bros." abbreviation under SMB3. As far as I knew there were only two versions (click for larger images):
NES-UM-USA:

and
NES-UM-USA-1:

The "Bros." moves from one side of the logo to the other - that's how you can tell the two versions apart at a glance.
But now there's a third version???
Darn, I would have liked to pick that up, just to check it!
From what I can see in the picture, it also looks like a NES-UM-USA-1.
If anyone knows anything about the cart with "Bros." in the middle, or if you see another one, let me know.
Does anyone know of an international version with "Bros." in the middle?