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Yeah...that bit is kind of key here...

You have until 1 year after purchase to add AppleCare to the computer. Your best bet is to go to an Apple store or call AppleCare support and give them your serial number and what not and they may be able to lookup the sale date.
 
Sounds like Best Buy didn't transmit the purchase date information to Apple.

Please call 800-APL-CARE and have your original Best Buy receipt handy. They will need to properly register your computer.
 
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