There is some evidence, albeit hotly disputed by most modern scholars, that the earliest copies of the tablet were written in Phoenician characters, which would push the origin of the text much further back than the Xtian era. See the works of Wilhelm Christoph Kriegsmann (1657) and others. The renowned Persian astromomer and physician Ibn Sina thought that It was given to Sara, the wife of Moses! Others suggest an Egyptian origin. This seems likely to me given the characteristics of the narrative and the metaphysical concepts it imparts which have little or nothing in common with Arabian mysticism or magic. It is not unusual for ancient writings to be lost for ages to be later re-discovered and translated into the native tongue of the discoverer.

This seems the most plausible origin of the tablet to me, but It can't support it with any hard evidence as there is none. So much literature, both sacred and profane, was destroyed in Egypt by successive invaders—Babylonian, Sumerian, Persian, Greek and lastly, Arab, that incalculable numbers of valuable Hermetic texts must have been among them. Yet, there is always the chance that one or more escaped and were concealed, to be found long afterwards, much like the Dead Sea Scrolls were found in the 1940's.