The source of my information is examining literally hundreds of Mark I rifles from when I worked as a volunteer at the CMP.
All Mark I rifles went through WWII. The very large majority of them got overhauled and refinished. Most got re-barreled with 1942-dated barrels. The survival rate of original examples is very small. And those with the black paint still intact are virtually non-existent.
Be aware that some Mark I rifles were overhauled and refinished in batches during WWII. And got their Mark I parts re-installed back on them. So, there are some Mark I rifles in circulation that look original but, in fact, are not. The CMP, for example, just auctioned one. And that's how they found it.
I'll search my files for photos.
J.B.