Originally posted by PsychoPawn
I'm guessing the simplest explanation is just that someone with access to them at some point was able to swap it out either before it was given.
I was an Apollo tech at Goddard Space Flight Center back in the day, Apollo tracking and timing (atomic clocks) and through an interesting circumstance, was allowed to hold one of the moon rocks held in the giant vault at Goddard and I can tell you if I had seen that rock given away, I would have surmised immediately it was fake. The real ones look really alien.