Nintendo was accused of antitrust behavior because of the strict licensing requirements. The United States Department of Justice and several states began probing Nintendo's business practices, leading to the involvement of Congress and the Federal Trade Commission (FTC). The FTC conducted an extensive investigation which included interviewing hundreds of retailers. During the FTC probe, Nintendo changed the terms of its publisher licensing agreements to eliminate the two-year rule and other restrictive terms. Nintendo and the FTC settled the case in April 1991, with Nintendo required to send vouchers giving a $5 discount off to a new game, to every person that had purchased a NES title between June 1988 and December 1990. GameSpy remarked that Nintendo's punishment was particularly weak giving the case's findings, although it has been speculated that the FTC did not want to damage the video game industry in the United States.
 Who didn't interview retailers as part of their investigation?