We don't have very good ways to determine how old stonework is, in general. The convention for dating Egyptian works is to date them by whichever is the oldest name somebody carved into them, or by the age of objects found buried nearby. Carving a current pharaoh's name into older stonework, and chiseling away previously carved names, was absolutely the norm, with many things peppered with such alterations. But the obviously oldest things were all made with no name carved in. Often the alteration used to date one is comically cruder than the object itself.

In the only published use of surface luminescence testing applied to Egyptian stonework, it seemed to date a fragment of a facing-stone block from the presumed most recent of the Giza pyramids to 500 years before its official age, albeit with error bars that just barely included the official age. Surface luminescence is a technique that determines when a rock surface was last exposed to light. If the sample is collected with insufficient care, the test will indicate a more recent date than would be correct. It is frustratingingly imprecise, dating the sample in question to 3000 BC, +/- 500 years. No further such work has been permitted.

We actually have documentary records from the supervisor of a crew that received facing stones for work on a pyramid, but we do not know whether the stone was for repair or improvement, or original construction. Pharaohs frequently boasted of repairing or improving older works. The pharaoh officially credited with making the Sphinx left a stela next to it describing the improvements and repairs he had commissioned.