If you look at the rivets on the smokebox front of 560, and then try to line them up with the adjacent rivets on the smokebox wrapper (a bit like "joining the dots"), what you get is a zig-zag pattern, hence staggered. Most people won't be too fussed about this, and that's fine, but it is something I noticed and since I have a rivet press I might as well give it some proper work to do!
GSR/CIE really were great believers in rivets - smokeboxes were absolutely covered in them, and it can be a total pain in the **** when you're trying to get it right. The other thing I have to try to do is calculate how many rivets there are around the smokebox front of 560.