Yeah, 2 is typical, on a Betax shutter anyway. I didn't know they put 2 on the Supermatic. Leave it be, it's no mistake. One is on top of the blade stack and 1 at the bottom of the stack. This is to be sure the shutter really is light-proof when it's closed. Otherwords, light would "leak around" the next lowest blade from the top of the stack without it, and the shutter would be worthless for walking around in the daylight without a lens cap.