C14 dating oddity

Bob Porter over at the New Chronology Yahoo group has written that C14 dates from Thebes differ from those of the same period taken from Tell ed-Dab'a – by as much as a century. One theory being advanced is that delta water contains more older carbon than the Nile near Thebes (but plants are supposed to absorb C14 from the atmosphere). We seem to have something that might be explained by C14 samples being analysed at different laboratories – which would have to be explained in more detail. It remains to be seen if archaeologists and scientists bother to look into the issue as it must have been endemic (older dates) and may cause more trouble by dredging up than leaving alone.