Huummm.
Seems like kind of a strange system. Why would there be the need for a third number?
Typically frame and motor numbers match, but not in all cases. But why would you ever need a third number on a bike to identify it legally?
Here in Indiana the VIN is always the frame number which on most Japanese bikes is typically located on the head tube.
That's the legal deal here. That's the number that goes on the title.
You could interchange 6 different motors on that frame and completely change all other parts, but that vehicle would always be legally what the frame number is.
That's part of the reason I occasionally see frame for sale ads where the owner emphasizes he has a title to it. It's a bit of a sales positive.
If you have a matching title and frame number, you have the basis for a total rebuild to register and plate, if that what someone's inclination would be.
If you have a frame here, but no title to it, you're essentially screwed as far as titling, registering, and plating a street bike. It's a huge expensive hassle to get around that in Indiana.
Regards,
Steve