GR: Thanks for that explanation. You begin with the hypothesis that "1534 [is the] Year of the birth of Hatshepsut." I still don't see why Senenmut would construct an astronomical ceiling in one of his own tombs to celebrate the birth of Hatshepsut. Isn't it his tomb? And doesn't the ceiling record a singular astronomical event, and not just any old date -- meaning that if it does, by coincidence, celebrate someone's birth it would be his own? Maybe it was Senenmut's ability to foretell (or even just to illustrate) this astronomical alignment as a young man that earned him a position in the King's court, eh? Anyway, all I meant was that Senenmut could have been much older than Hatshepsut.
ML: This particular tomb of Senenmut is *within* the environs of Hatshepsut's own mortuary temple in the Theban necropolis! Hatshepsut was Senenmut's royal mistress, the one he supported and to whom he owed everything. Nobody I know of had more titles [and more extant statues] from that reign than Senenmut. Separating the northern and southern skies on that ceiling are some bands of text and, separating those bands, in the largest hieroglyphs, are the titles and cartouche of Hatshepsut.
Now, it is quite evident from the tomb of Senenmut's parents that, before his rise to Hatshepsut's "favorite", his family had been quite poor and his father a nobody. Of the persons in that tomb, the only one who had a relatively rich interment was Senenmut's mother, who had obviously lived long enough to see her son grow prosperous. The others, including the father, had nothing, not even a proper mummification. Obviously, their remains had simply been gathered from somewhere else and placed in that little tomb with Senenmut's mother when she died. If I am correct and that ceiling reflects someone's birthday, it would be more likely that it was Hatshepsut's--she of the so-called "divine birth", her mother having been impregnated by the god, Amun, in the guise of Thutmose I. More practically, it would have been far more likely that the birth date of a girl whose family was so close to royalty would have been recalled than that of a son of poor folk. Since such births were not recorded in any bureau, it's even possible that Senenmut didn't know the date of his own birth.
If records of the heavenly bodies were kept [and the ancients claim the Egyptians were wonderful about that] then they would probably have been dated by the priestly calendar, as the priests were in charge of such things. But their calendar, being about festivals, co-existed with the civil calendar. Regardless of all that, I think Hatshepsut would have known in what year of what king she was born [as Senenmut would have, too] but even what day of the month--could have found that out by some means or another.
Do I have any way of knowing for certain that the ceiling depicts Hatshepsut's birthday? Of course not! All I tried to show is that, if the date of von Spaeth is correct, then that is not a far-fetched reason for it, according to a chronology I can accept.