Ahh all those look about the right size. Check these babies out
The bottom border on the Zeider is huge and the top isn't short. Same goes for the Schupp alough it isn't as big. The Schang was certainly cut down.
All three of these cards seem to be cut on all sides and certainly not machine cut. They certainly doesn't seem to match the above cards.
Is it possible that one central company produced the cards with black backs and that the BS and CM are stamps that the specific companies used?
James G