Hello Dan-San,
Sanke # 450 (photo 1) was taken around 2 -3 February 1917, on the occasion of MvR having received PLM on January 12, 1917. Sanke #503 was taken at the same time, as well as photo #3. There is a very nice discussion about these Sanke cards on Lance Bronnekant book:
The Imperial German Eagles in World War I: Their Postcards And Pictures, Vol 1. I recommend Vol II as well.
In these photos, especially #1, we see MvR wearing the formal dress, Dunkelblau (dark blue) Ulanka. We can clearly see the epaulettes with the Kaiser Alexander III monogram.
Blue skies, Dan-San
George