Its the company that promises it, in exchange for the free concert, they want fans to buy as much as possible. They would earn big time this time fi they hit 500,000 since the Jewelry Box albums are not cheap at all. Oh well i'm sure it'll hit anyway seeing how T-ara is so successful in korea and japan not to mention international fans like me are probably dying to get every edition possible for all their albums, but at the same time a part of me saying 500,000 is an impossible number to hit due to the pricing, CCM still assumes T-ara fans are all rich peeps.
But honestly i rather CCM promises T-ara a 1 month break if 500,000 copies were sold, X.X overworked idols + free concerts, don't match.