Not sure what's going on, going through the tutorial series for SD4 with SD5. I've noticed when in the video 'Exposing Parameters...', that while the base color, roughness, and even metallic, are impacted by the Material Color Blend node when adding the Ground Dirt Mask, it doesn't seem to be doing anything with the Normal channel.
In the picture below the parameters are for the Material Color Blend Node, and the 2D view is of the final Normal Map, lacking any modifications from the dirt mask of the material color blend... What's up here? And again, the other channels are fine.