The Tab.Heracl. have τὰν (δὲ) νᾶσον as 'alluvial land' (LSJ s.v. 2) in 1.38 (= Buck, no. 79, p. 274 and, for the gloss, p. 280) and an inscription from Karpathos has ἐπὶ τὰν νᾶσσον (153 BC).
LSJ's papyri: land flooded by the Nile, PHib. 1.90.7 (iii B.C.), etc.; opp. ἤπειρος, PGiss.60< 4.12 and 5.1> (ii A.D.); νῆσοι ποταμοφόρητοι POxy.1445.13 (ii A.D.)