First of all, as seen in the relevant portion of the Warren Commission Report below, the unidentified print was a PALM PRINT, not a fingerprint. How someone can believe a palm print is a fingerprint is beyond me. A "print" can refer to either a palm or a finger print. If you have ANY proof it was a fingerprint, please provide it. It certainly does not, as you claim, appear in the Warren Commission Report.
Here's what Darby himself said about the matter: Darby told Vincent Bugliosi that he had been given "two fingerprints, one from a card, the other a latent. It was all blind. I didn't know and wasn't told who they belonged to (it was much later, he said, that he heard Malcolm Wallace's name mentioned), although I recognized the layout of the card (he said all identifying features had been blacked out) as that of the Texas Department of Public Safety. I wasn't given any palm print. They were both fingerprints. Of course, you can't compare a palm print with a fingerprint." (Reclaiming History: The Assassination of President John F. Kennedy, pgs. 922-923).
In other words, Darby was duped...and, by extension, so were you.
http://mcadams.posc.mu.edu/russ/jfkinfo/wcr6.htm#p5"In considering the possibility of accomplices at the window, the Commission evaluated the significance of the presence of fingerprints other than Oswald's on the four cartons found in and near the window. Three of Oswald's prints were developed on two of the cartons. In addition a total of 25 identifiable prints were found on the 4 cartons. Moreover, prints were developed which were considered as not identifiable, i.e., the quality of the print was too fragmentary to be of value for identification purposes.
As has been explained in chapter IV, the Commission determined that none of the warehouse employees who might have customarily handled these cartons left prints which could be identified. This was considered of some probative value in determining whether Oswald moved the cartons to the window. All but 1 of the 25 definitely identifiable prints were the prints of 2 persons an FBI employee and a member of the Dallas Police Department who had handled the cartons during the course of the investigation. One identifiable palmprint was not identified."
If that's not enough, the following link will take you to CE3131, a letter from the FBI to General Counsel Rankin noting that the only print remaining to be identified was a PALM PRINT. So much for your goofy claim.
http://www.history-matters.com/archive/jfk/wc/wcvols/wh26/html/WH_Vol26_0418a.htm