Complete VINs are on every body panel on the cars, and on the VIN plate attached to the firewall (base of windshield) and the VCL (door sticker).
Partial VINs are on the body/buck tag, engine, transmission, and tags welded to each inner fender (requires removal of outer fenders to read).
When you said neither comes back as stolen, how did you figure out the entire VIN from the body/buck tag? It won't come back as stolen if it's not even a correct VIN. To know the VIN check digit (9th position) you have to know all of the rest of the 16 postions of the VIN, and then the check digit is calculated by an algorithm.
1979-1993 Fox Capri and Mustang VIN Decoder: foxchassis.com
Wanted (Dead or Alive): VINs, Vehicle Certification Labels, Buck Tags, Build Sheets, Window Stickers, Owner Cards, Warranty Tags, History 999 Reports, Invoices, Axle Tags