See the Big West sticker. Even the DVD jacket for the Japanese release markets it as part of the Super Dimension Saga along with Macross and Orguss. You can even find Southern Cross on Big West's website. I think the situation is reversed with Southern Cross. All of the design work was done by Tatsunoko's design studio, Ammonite and it was animated by Tatsunoko with Big West handling the production and marketing side. It may only apply to Japan, but Tatsunoko clearly does not have total control over Southern Cross like it does Mospeada.