You could and likely have looked up information about that which you ask.
Even the simple wiki article on the subject Axial Precession is rather comprehensive about what is known
Axial Precession is unproven. "Sealing the deal" on an unproven assumption is not scientific. As I have endeavored to highlight, Axial Precession may not exist. Other forces could be at play.
there is little reason to suspect it would be a massive departure from the range observed for well since the Greeks 2000 plus years ago.
Not sure what you mean here. Are you suggesting that because the phenomenon of Precession has been measured for 2000 years then that, in a dynamic universe, this measurement can be extrapolated back in time to (Name a Date) with accuracy?
You know darned well there is no known evidence of any civilization lasting for 26000 years and recording periodic precessions. The estimate is made by observing smaller chunks of time.
Somebody seems to think otherwise.
We know this, because at the end of last year, with the help of Alistair Coombs, I proved, in a scientific sense, that these animal symbols, in Western European cave art at least, can be interpreted as the same constellations evident at Göbekli Tepe, which in turn are the same as the ones we use today.
Of course, some of the symbols have changed over the intervening 40,000 years. For example, it appears that for at least 30,000 years, the feline symbol was used to represent the constellation Cancer, and likewise the bovine symbol was used to represent Capricornus.