  Magnetoresistance measurements have been carried out along the highly
conducting a axis in the FISDW phase of hydrogened and deuterated
(TMTSF)$_2$ClO$_4$ for various cooling rates through the anion ordering
temperature. With increasing the cooling rate, a) the high field phase boundary
$\beta_{\rm {HI}}$, observed at 27 T in hydrogened samples for slowly cooled,
is shifted towards a lower field, b) the last semimetallic SDW phase below
$\beta_{\rm {HI}}$ is suppressed, and c) the FISDW insulating phase above
$\beta_{\rm {HI}}$ is enhanced in both salts. The cooling rate dependence of
the FISDW transition and of $\beta_{\rm {HI}}$ in both salts can be explained
by taking into account the peculiar SDW nesting vector stabilized by the
dimerized gap due to anion ordering.
