  We present a reanalysis of CDF data to extend limits on individual
fourth-generation quark masses from particular flavor-mixing rates to the
entire space of possible mixing values. Measurements from CDF have set
individual limits on masses, $m_{b'}$ and $m_{t'}$, at the level of
$335$--$385$ GeV assuming specific and favorable flavor-mixing rates. We
consider the space of possible values for the mixing rates and find that the
CDF data imply limits of $290$ GeV and greater over a wide range of mixing
scenarios. We also analyze the limits from the perspective of a four-generation
CKM matrix. We find that present experimental constraints on CKM elements do
not suggest further constraints on fourth-generation quark masses.
