On pg. 23 n. 2 I mention Hartmann's vindication of the genuineness of the Praenestine fibula and its inscription. This famous inscription (MANIOS MED FHE:FHAKED NVMASIOI), if genuine, would be our single oldest piece of Latin. Hartmann—to the extent that I am qualified to judge—seems to make a good case that the scientific testing supposedly proving the falsity of the document was flawed or inconclusive, but the form NVMASIOI still seemed a bit of a problem. Numasios would appear to be the ancestor of praenomen Numerius, but Numerius if related to numerus 'number' should go back to *numesios vel. sim. So either (1) Numasios is not the ancestor of Numerius, (2) Numerius has nothing to do with numerus, or (3) the fibula is a fake. Possibilities (1) and (2) are perfectly plausible, so no strong argument against the genuineness of the inscription can be drawn from the form NVMASIOI, but recent developments have put to rest any doubts about this name.
Through the kindness of Rex Wallace I've been informed about a recently published archaic Etruscan inscription on an aryballos from the "area ceretana" bearing the inscription (Poetto and Facchetti 2009:369):
mi mlac mlakas larθus elaivana araθia numasianas
‘io (sono) il buon/bel (vaso) oleario di Araθ Numasiana per il buon Larθu’.
The form numasianas supports Numasios and makes it certain that Numasios is unconnected with numerus.
Poetto, Massimo and Giulio Facchetti, 2009. L’aryballos di Araθ Numasiana. Oebalus 4:365-384.