Note the websites of the dubbing companies but also check in with Anime Networks or here for updates, since licenses change.
Dubbing is kind of dying out. Dubbing costs more and takes longer as they need to rewrite the scripts for the English translation to make sense and lip-sync with the characters. Subs are just translations and text. Most fan groups can turn out an episode subbed in three days at least and that's doing it part time.
Plus, long running series are not always going to get covered totally unless interest keeps up.
Just looked it up, 1-4 were licensed by Funimation and stage 4 was broadcast PPV via Animax.
I also saw that the series just caught up with the manga and there are no more stories to adapt. And here I thought the 5yr break between 4th and 5th was enough