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.