Platinumed GOW today. Finding the ravens is a pain because I only needed like 15 but had to follow a guide from the start because you don't know which ones you need. They really should have made it possible to buy a treasure map post game revealing where they are. Because what's the point in making the player use a YouTube guide.
Maybe as a reward for finding the 12 hidden treasures give a map for the ravens.
On the map you can see the items per region. That helped me a lot with finding my missing artifacts.