I am Region 4 as well.
When I first got the Trilogy, it stuffed up at the end of Godfather 2. When Sonny spoke the whole thing pixellated and froze.
I returned it and got instead a perfectly good disk set.
I have a feeling the appalling packaging of the Trilogy allows the disks to "go bad". I have yet to see a copy of the GF films in which the cardboard DVD holders aren't creased and bent.
My previous batch, the older batch, had a matte surface on the upper side of the discs, while the new batch has shinier upper sides. Don't know if thatll help...