  We review $CP$-violating observables in flavor tagged and untagged $D^0
\rightarrow K^{-}\pi^{+}$ decays and evaluate the $CP$ asymmetry difference
between the two decays. We note that this commonly neglected difference is not
zero in principle and can be significant in future $B$ factory experiments. We
also construct an expression to extract the strong phase difference between
$\bar{D}^0 \rightarrow K^-\pi^+$ and $D^0 \rightarrow K^-\pi^+$ decays,
independently of existing experimental methods.
