The quickest, easiest thing to do is look for the date that the metal went though the stamping plant. Should be around the latch striker pin. Can't remember exactly where (it has been awhile since I have gone over my 72'). Most body panels will have stamping dates on them (doors, front fenders, hood) dates may be off by a few days, but it is a quick way to see if there had been any body panel replacement.
For years the 69-70, and 71-73 Mustangs have been overlooked due to the popularity of the 64 1/2-66, and 67-68 Mustangs. The past few years the are starting to come into their own. You can get info on your Car by Calling/E-Mailing Mardi with the VIN number. They have access to Ford data bases, and can give you complete info on your Car as it was built.Don't have the contact info close at hand (Calling Dan Martorano!!). There are books out to help you decipher the Cars data plates.