The exact process by which Fishler identified the copy as the one stolen from Cage is not described in detail in the available reporting. The ABC News account says the comic was “later discovered to be” Cage’s, without specifying the identification process. The Duluth News Tribune account says Fishler “authenticated” the comic as the copy he had sold Cage. Authentication in this context would have involved familiarity with the copy’s specific physical characteristics—the CGC certification number and encapsulation, if it remained in its CGC holder, or the specific condition details that Fishler would have noted at the time of the original sale.
CGC-encapsulated comics carry a certification number that is recorded in CGC’s database alongside the grade, the issue, and information about the copy’s submission history. If the stolen copy had been graded by CGC before the theft—and the CGC UK account indicates it had been graded 9.0—the certification number would have been a reliable identifier. A comic in a CGC holder with a specific certification number is verifiably the same object that was graded with that number, unless someone had cracked the case and replaced the contents, which is a form of fraud that CGC’s cases are designed to make evident.
The Duluth News Tribune account also notes that the comic was held as evidence in an LAPD safe during the investigation. This is the standard procedure for stolen property recovered in the context of an ongoing investigation: the object becomes evidence in the case, and its status as evidence supersedes its status as personal property until the investigation’s needs are satisfied.