The frame number tracking was a favorite tool of Don Dover at X2200 South. Once the builder's number was lost then everyone wanted some means to identify the rebuilt ICG locomotives, the frame number became that tool. When the IGC rebuild program was in full bloom, Gary and I spent many hours recording frame numbers at Paducah. As the ICG expanded the program and bought locomotive "cores" from where ever they could find them, the components became so mixed that in fact the rebuild was in effect a "new" different locomotive.
The frame number was a production/inventory control tool for EMD when the locomotives were being built. The same number appeared on the long and short hoods the cabs and most likily other componets. In the end however, it was the builder's number that identified the specific locomotive.
If you have a basically as built EMD locomotive with the builder's plate missing, the frame number can be a useful tool for identification.
So while the use of the frame number tracking is of some value, if you have an ICG GP-10 with a C&O frame number, a UP powerplant, ATSF traction motors, NYC main generator,the long hood from B&O unit and a short hood from NH with a cab from QNS&L, you do have a locomotive for sure but it's a stretch to say it was any specific locomotive.
