In 1970, 4967 sets were issued containing silver that was thought to have been carried around the moon. After learning this to be incorrect, requests were made to return the medals. A replacement medal was then sent back to the subscriber that contained some silver that was flown aboard a mission. A line was put above the mint mark to distinguish it from a set that was not returned. Franklin Mint reported 3698 sets were returned. Variety 1Regular mint markVariety 2Line above mint mark The Project Apollo medal set contains 20 limited edition medals presented to Apollo astronauts and direct supporters of America's space program. Each medal contains silver from other medals personally carried by the Apollo XIII astronauts on their April 11-17, 1970 moon-flight.https://library.princeton.edu/libraries/firestone/rbsc/aids/newman/newman5.html (1970-12-28)https://www.worthpoint.com/worthopedia/project-apollo-man-greatest-adventure-677557551