If you look at the photo below, notice how all of the bricks run in the same direction. In most construction, the every 5th course of bricks will be turned and laid over both the face and inside brick. Another construction method is to use what is called a brick tie that sits in between bricks. Both of these methods are used to prevent the brick from falling off the wall.
So the areas of brick where the mortar is whiter is original? There appear to be header courses in those areas. Have you confirmed that there are no brick ties in the new construction? Are you probing? I'll save the rest of my questions for offline.
Great question, the next step was in fact to probe the space and verify if brick ties were installed or not, but you'll need to read the next post to find out!