>>91665807 She only became "one with the Phoenix" the first time she died ... or technically was about to die ...
And she was split into two people when The Phoenix did that, one being placed inside a protective cocoon that was soon lost and the other becoming (merging with) Phoenix.
Phoenix-Jean then died on the moon by suicide after going Dark Phoenix once too many times and Non-Phoenix Jean went on to live a relatively long life until the Morrison run, where she died twice.
That should be all of it.
(unless I'm forgetting a death or two)
