You can use the /g modifier, and replace the if by a while (untested):

for (@Read){
    while (m/Number-(\d{4}-\d{4})/g){
         print "$1\n";
         print WR1 "$1\n";
    }
}
[download]

By putting the parenthesis only around these parts of the regex that you want to capture, you avoid the substr alltogether.

\d{4} is short for \d\d\d\d