Most of the sets are missing a couple of small pieces, I will list what I know is missing but there may be other pieces missing as well

NMPD Pelican: missing a couple of blue-gray 1x4s on the underside of the wings, a vent piece on the top of one wing, and of course the landing pad

Warthog: missing the gas cans

Gausshog: missing the sight on the gun and the gas cans

Banshee(newer version): missing a couple of semi-circular pieces on the rear

Seraph: missing 2 fin pieces

Red Chopper: missing the gun pieces on the sides and the foot rests