use English qw( -no_match_vars );
...
my $bates_number_pattern = qr{ ... }x;
...
sub parse_bates_number {
    my $bates_number = shift;

    $bates_number =~ $bates_number_pattern
        or die "Invalid Bates number: $bates_number\n";

    return map  { substr $bates_number,
                         $LAST_MATCH_START[$_],
                         $LAST_MATCH_END[$_] - $LAST_MATCH_START[$_] }
           grep { defined $LAST_MATCH_START[$_] }
                ( 1 .. $#LAST_MATCH_START );
}
...
    my ($prefix, $number) = parse_bates_number($bates_number);