In the 1960's I noticed once in a while on flat press printed plate number singles (and larger pieces) sometimes the reverse would show negative images of another plate number (sometimes the same plate number).
I expect this reflects that presses were side by side and were hand feed. (that's my guess).
This might be a way to find rarer plate numbers.
Has anyone else discovered this besides me?
Let's see other examples.
Attached is 512 with this right and proper example.