Why does it show im missing 1 weapon but when you go to the shop you bought them all in assassins creed2

There is a secret weapon you unlock after you collect 50 feathers. There is also another secret weapon but you have to buy it. It comes available after you get Altair's Armor. If the first two answers were wrong, it's probably downloadable content from the psp game: Assassin's Creed: Bloodlines.