I thought the same thing when I first bought it, but the gentleman at the gunstore was telling me that the Centennial Edition was a limited run from 1909 to 1912. The primary difference that I've noticed is some of the stamping on the receiver and the British coin that is set in the stock.
Item Name: FS/FT Lee-Enfield No.3 Mark 4 SMLE Centennial Edition
Location: Gainesville
Zip Code: 30504
Item is for: Sale or Trade
Sale Price: 450
Trade Value or Items Looking For: 600
Caliber: .303 British
Willing to Ship: No
Bill of Sale Required?: No
Item Description: Up for sale or...