What is Non-total reaction, final extent ratio?

Example 43.2 (An ester that stops halfway)

Heated with $1\,\mathrm{mol}$ of ethanol, $1\,\mathrm{mol}$ of ethanoic acid forms ethyl ethanoate and water, $\ce{CH3COOH + C2H5OH <=> CH3COOC2H5 + H2O}$. The reaction stops when about two thirds of the acid have reacted: $x_f = 0.67\,\mathrm{mol}$ for $x_{\max} = 1\,\mathrm{mol}$, so $\tau \approx 0.67$. Starting from $1\,\mathrm{mol}$ of ester and $1\,\mathrm{mol}$ of water, the reverse reaction also stops, with about one third of the ester hydrolysed: the same final mixture.