...
    if (defined $flag_assignments{$temp_key}) {
        print "KEY [$key] TK [$temp_key] TS [$temp_semester] FAS [$flag_assignments{$temp_key}{starrez}] FAA [$flag_assignments{$temp_key}{abbreviation}]\n";
    }
    # Here it is possible that $flag_assignments{$temp_key} does not exist
    
    
    # ONLY ONE FLAGE PER CATEGORY, AND GREEKS LIVING ON CAMPUS WILL ALSO GET NR ACCESS TO THE HOUSE OF THE FRAT/SORORITY

    if ($starrez{$key}{"dorm"} ne "None") {
        # Here, autovivification of a value for $flag_assignments{$temp_key} happens
        # because it's part of $flag_assignments{$temp_key}{$temp_semester}
        if ($flag_assignments{$temp_key}{$temp_semester} ne "") {
...