Jeff, you are quite right that Mars is missing from Senmut's ceiling. Sorry, Avry, but von Spaeth's article has been throughly trashed elsewhere for its astronomy AND its Egyptology. The interpretation of a decan as Mars is indicative of von Spaeth's ignorance. His take on the ceiling doesn't hold up anyway you look at it.
These ceilings are difficult to interpret as pictures of an actual sky. If this were such a picture, there is a reason Mars is missing, and any attempt to see this as a readable date must take missing Mars into account.