  Tau-based finite-energy sum-rule (FESR) analyses often assume that scales
$s_0\sim m_\tau^2$ are large enough that (i) integrated duality violations
(DVs) can be neglected, and (ii) contributions from non-perturbative OPE
condensates of dimension $D$ scale as $(\Lambda_{\rm QCD}/m_\tau )^D$, allowing
the OPE series to be truncated at low dimension. The latter assumption is not
necessarily valid since the OPE series is not convergent, while the former is
open to question given experimental results for the electromagnetic, $I=1$
vector ($V$), $I=1$ axial vector ($A$) and $I=1$ $V+A$ current spectral
functions, which show DV oscillations with amplitudes comparable in size to the
corresponding $\alpha_s$-dependent perturbative contributions at $s\sim2-3$
GeV$^2$. Here, we discuss recently introduced new tools for assessing the
numerical relevance of omitted higher-$D$ OPE contributions. Applying these to
the ``truncated OPE'' strategy used in Refs.[1,2] and earlier work by the same
authors, we find that this strategy fails to yield reliable results for the
strong coupling from hadronic $\tau$ decays.
