The Sana manuscripts is a palimpsest manuscripts ; which means that there is a lower and upper layers of writing . Scholars say that the two writings are late seventh and early eighth century respectively.  They think that it is two versions of the Quran; the first is a pre- standard Quran which was erased and rewritten as the canonical version.  On comparing the two writing , it was found that there are seventy variants between the two.  Dr Jay says that the lower text was erased because it needed to be updated.