Thurs Nazir 61

The gemara ends by saying that a Nazir Tamai needs a razor from our case of the Safeik Nazir Tahor or Tamai

Tosfos asks, how is that a proof. Perhaps he needs to shave his hair for the chance he's a Nazir Tahor? Tosfos answers: since we don't allow him to drink wine and needs another period to act like a Nazir and bring other Korbonos (where he'll shave his head anyhow for his Nazir Tahor) So we wouldn't acquire him to do so the third period if not that even a Nazir Tamai needs a razor.