Bill and Harold only throw one glider apiece, and Harold's glider clearly falls to the ground after "boomeranging" back and bumping into him, yet two gliders then run into Harold and Bill.
Bill has only a standard rubber band on his wind-up toy plane, yet in the close-up shot of the "extreme winding" scene, there is a humongous long rubber band that had balled itself up into an enormous thick tangle --- far more rubber total than a simple little elastic band would contain.
The huge amount of rubber-band material shown on Bill's wind-up plane would be far too bulky/heavy for the plane to get airborne.
Obvious spherical ball of string/rubber bands included in the lower part of the tangled rubber band on Bill's toy plane.
Red says, "The gliders have finally spent their elastics", yet the toy planes shown are just that --- gliders --- which merely have single-piece weighted tips and are meant to simply be tossed into the air, and so they do not have rubber-band-powered propellers.