Progressive Revelation.

No spiritual teaching is ever set in stone.
There is always the possibility that a more advanced teaching can be given as people raise their consciousness.
The essence of progressive revelation is that it is ongoing, it will never stop, so no spiritual organization can claim that they have all there is to know.
This revelation is also progressive and deeper levels of understandings can be released as people show their willingness to reach for MORE.
The Ascended Masters are the spiritual teachers of humankind and they have released various teachings at different times in order to reach different audiences who are at different levels of consciousness.
But as people raise their consciousness, the Ascended Masters can release teachings that go beyond those previous teachings and help people to reach for MORE.
So it is advisable to be open-minded and always be willing to reach for More.