Mithrandir said:

I guess no rpvee, I think Ady might be referring to a common PT "plot" phase, where all three movies could be worked as a whole in order to improve the story arc and see what works and what doesn't, while there could still be a time after that, when the movies are treated individually, a "technical" phase (?) concerning the "classical" revisited job (enhancing mattes, Colour Correction, etc.)

But ofc, I'm just guessing, Adywan has the real answer.

That's a good point too. But you're right, Ady has the real answer.