In "Tony Hawk's Underground" For Xbox, Why Can't I Edit Certain Tricks?

I know this is a REALLY old game, but every time I bought a new console, I bought a copy of this game.I bought an Xbox 360 Elite in December of 2009, and just bought a copy of the game for Xbox (from the flea market). I LOVE the "Create-A-Trick" mode, but I notice that certain moves for certain characters are not available to edit, because their not a part of the create-a-trick menu. For example, Iron man's manual scanner, and Gene Simmon's lick it up grab, and even Gene Simmon's "Fire, Fire, Fire" grind.