  New rate measurements of $B^0$ decays into $\pi^0\pi^0, \pi^0\eta,
\pi^0\eta', \eta\eta, \eta\eta', \eta'\eta'$ and $K^+ K^-$ are used in
conjunction with flavor SU(3) to constrain the coefficients $S$ and $C$ of
$\sin\Delta mt$ and $\cos\Delta mt$ in the time-dependent CP asymmetries of
$B^0 \to \eta' K_S$ and $B^0 \to \pi^0 K_S$. Experimental values of $S_{\eta'
K}$ are now seen to be closer to the Standard Model expectations, fully
consistent with the new improved bounds.
