1) It is common practice to name new places with old names: take for
Londonderry, N. Ireland,
Londonderry, Nova Scocia,
Londonderry, New Hamshire,
Cape Londonderry, Austrailia
Isla Londonderry, Chile.
Therefore it would not be surprising to find both pre-flood Tigris and
Euphrates rivers and post-flood Tigris and Euphrates rivers. These need
not be the same rivers at all.
2) There is literary evidence in Genesis that Moses edited Genesis from
about 11 family histories which were likely written on clay tablets in his
day, but which had likely originated as oral family histories. Thus the
references to geographical features in the stories may not be Moses'
identification of locations at all, but rather that of the originators of
the family histories.