There are 13 known different US versions of the VertiBird playsets. The original VertiBird had an early manufacturing change that modified the drive spring to drive rod coupling. The first version had the end of the drive rod screwed into the drive spring on the helicopter. The production modification resulted in the drive rod being permanently soldered to the drive spring and packaged the base, controls, rods, and helicopter (except the rotor) into one complete unit.
