for my $c1 (keys %hash) {
        for my $c2_c3 (keys %{$hash{$c1}}) {
            my ($c2, $c3) = split('_', $c2_c3);
            if (
                () # $c2 is ok
                &&
                () # $c3 is ok
            ) {
                # do stuff for good data
            } else {
                # do stuff for bad data
            }
        }
    }