  Advanced LIGO and Virgo detected ten binary black holes (BBHs) in their first
two observing runs (O1 and O2). Analysis of these events found strong evidence
for a dearth of BBHs with component masses greater than $\sim45 \ M_\odot$, as
would be expected from a pair-instability mass gap. Meanwhile, a standalone
analysis of the merger GW170729 found its primary mass $m_1 =
{51.2^{+16.2}_{-11.0} \ M_\odot}$, with the majority of its posterior support
at $m_1 > 45 \ M_\odot$. Although this appears to be in contradiction with the
existence of a limit at $\sim45\ M_\odot$, we argue that individual events
cannot be evaluated without reference to the entire population. When GW170729
is analyzed jointly with the rest of the detections, as part of a full
hierarchical population analysis, its inferred primary mass tightens
considerably, to $m_1 = {38.9^{+7.3}_{-4.5} \ M_\odot}$. For a large sample of
events in the presence of noise, apparent outliers in the detected distribution
are inevitable, even if the underlying population forbids outliers. We discuss
methods of distinguishing between statistical fluctuations and population
outliers using posterior predictive tests. Applying these tests to the primary
mass distribution in O1 and O2, we find that the ten detections are consistent
with even the simplest power-law plus maximum-mass model considered by the LVC.
This supports the claim that GW170729 is not a population outlier. We also
provide non-parametric constraints on the rate of high-mass mergers and
conservatively bound the rate of mergers with $m_1 > 45 \ M_\odot$ at
$2.8^{+5.4}_{-2.0}\%$ of the total merger rate. After 100 detections like those
of O1 and O2 from a population with a maximum primary mass of $45 \, M_\odot$,
it would be common for the most massive system to have an observed
maximum-likelihood mass $m_1 \gtrsim 70 \, M_\odot$.
