The fat bird was used on 64 and 65 models. The thin bird emblem was used starting in 66 and continued for several years after that. It encompases the emblems on the fender, the interior door panels, and the emblem in the center caps of the wheels/hubcaps. The thin bird in 66 was also on the dash and was located on the rear quarters instead of the front fenders.
Small grille emblem was only on the early cars. No definitive time as to when they switched to the larger emblem. Pretty safe to say the change over happened at different times at the different assembly plants--when they ran out of the small emblems, they switched to the new style.