It could have been a earlier war injury from circulation and then the devices all started flattening the longer it spent time in circulation. (Keep in mind other than years where a change over of design happens, most coins were not saved, but spent. Some where about 1934 they were started to be saved a little bit more rolls) Circulation on coins happened so much that a lot of the older ones would need to be counted as the edges on the wore down so much. If you put them into the coin rollers we have now, you'd be loosing money by selling them by the roll. (when the rims are worn off, the coin is a lot thinner)