Apparently a few of the Mickeys were damaged during shipment to the Disneyland Resort and at first were not put into DCA when the exibit began. Most likely they repaired those Mickeys and put them in with the rest of the Mickeys, only roping them off to try and keep people from climbing them and such, as kids typically do, and keep them from being damaged further. So that's my best guess as to the reason..
they were created for mickey's 75th birthday (last years attempt to rake major visitors into the parks) when they leave DCA they will leave for new york where they will be auctioned off and the money will be given to the person who desighned that mickey and then that money will go to his or her favorite charity.
hope that helps.
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