strange rear brake caliper problem

[AussieJohn]

Just fitted some spare rear uprights and found that the o/s caliper lower bolt does not line up. I checked 6 other spare rear calipers and found that the n/s calipers have a small part of the strengthening web machined out to allow more clearance for the bolt. None of the o/s calipers have this; I filed a little off the lug on the upright and it fitted OK. Anyone found similar problems?