The $1's have wide and narrow backs, but the change was in the vertical dimension...there's less green space at the top and bottom of the back design. The 1935D comes both ways, so check any 1935-35C note to see the wide back, and any 1935E-35H note to see the narrow back. The $1 faces didn't change. There were face changes on several other denominations, but they generally occurred between series, so they don't create interesting collectible varieties. For example, all 1928G $2's have a narrower (horizontally) face design than do 1928-28F $2's; this change just involved shaving off a bit of the outer webbed border, much like the change to the $10 backs. There was a big article about these changes somewhere not too long ago, but I can't remember now whether it was in Paper Money or Bank Note Reporter or where. Anybody track this down?