  Global gauge anomalies in $6d$ associated with non-trivial homotopy groups
$\pi_6(G)$ for $G=SU(2)$, $SU(3)$, and $G_2$ were computed and utilized in the
past. In the modern bordism point of view of anomalies, however, they come from
the bordism groups $\Omega^\text{spin}_7(BG)$, which are in fact trivial and
therefore preclude their existence. Instead, it was noticed that a proper
treatment of the $6d$ Green-Schwarz mechanism reproduces the same anomaly
cancellation conditions derived from $\pi_6(G)$. In this paper, we revisit and
clarify the relation between these two different approaches.
