Since the ether is commposed of T3 tiles stacked according to one of the two phases by which they can cover the plane, it might be tempting to call just any T3 an ether tile. To avoid such quibbles, a T3 is an ether tile only if it is part of an assemblage of T3's, especially when providing background.
By this interpretation, T3's may form part of composite tiles, and may have other tiles attached to them, without being ether. On the other hand, many interesting configurations exploit the versatility of considering boundary T3's as sometimes belonging to the ether and sometimes not.
A survey of all the de Bruijn diagrams for shifts through six generations not only revealed three of Cook's gliders, but also three more combinations interpretable as gliders against a background other than the ether. Continuing the survey for additional generations would undoubtedly reveal still more gliders, including the ones which have already been found via search programs.