Ok this is pretty much a word for word transcript of the response given by Ferne at the Las Vegas Fan Fest Lore panel (I took out the asides and uhms and ahs.). I will be pulling answers from this.
Only the One player character is supposed to be A Non-Padjal White Mage. Only they were chosen to receive their training from them. They have taught no one else.
They in this instances references the question asked, which was about the Padjal, so the revival is seemingly the One Player Character (see the point above.)
Other than Amdapoor, or the Padjal, there are indeed other groups trying to get White Magic, whether for themselves, or to simply cause chaos for the realm, we don't know, but the ways of getting it are nefarious.
So essentially, unless you found a Soul Stone in Amdapoor, or you have used nefarious means, it is outside of the lore. Note however, that outside of the lore does not mean Don't do this, or you can't do this, it does mean that there is no official cannon to support it. It becomes Grey Area that could very well have to be retconned by future reveals.