aside from the recent Hasbro one though, all their lawsuits predated the japanese court ruling that showed who owned what.
HG acted in accordance with what they believed their license to include in past lawsuits. that they did not legally have rights to all of what Tatsunoko gave them isn't going to be held against them for those past suits, because HG couldn't know at the time.
who does own the rights in question is an important issue in the current lawsuit however, and HG's past ignorance is no longer a defense, since they have had not only time to understand the japanese ruling, but also have completed arbitration with tatsunoko to sort out who owns what in america.