They may be the similar cels from the same 
animation sequence, like next or previous frame.
Remember, cels from the same sequence do look
alike with some slight differences.  Unless that
is a still frame, then there's only one cel to
it.  

If you remember the cel information like the frame
number on the top right corner (example: A3), 
then you can say it's the same cel.  Most likely,
both dealers got those cels from the same 
distributor.