1930 Model 25 motor numbers

Hi,  Some are aware I'm compiling a Flying Cloud registry.  In the course of doing that I see most 1930 Flying Cloud model 25 motor numbers begin with "2C", but two I have listed begin with "25S", one begins with "CD" and one with "CB", according to information found in the directory.  I suspect the last may be a motor number although it was in the serial number column.  But what about the others?  Can anyone tell me what the difference in the motors is, or the cars they are installed in, or why such different numbers were used?  You can also write at [email protected]
Thanks,
Carl