$data = array(
   '123456',
   '123457'
);


$new = array();
$data_tmp = $new;

while (1) {
   $test = array();
   $new = array();
   
   foreach ($data_tmp as $item) {
	   if (preg_match('/^\d{2,}/',$item) ) {
		  $suffix = substr($item,0,length($item)-1);
		  $test[$item][$suffix]+=1;
	   }
   }
   
     foreach (array_keys($test) as $base) {
		if (count(array_keys($test[$base])) == 10) {
            array_push($new, $base);
        }
        else {
			foreach (array_keys($test[$base]) as $k) {
				array_push($new, $base . $k);
			}
        }
		if (count($new) == count($data_tmp)) {
		   goto leavewhile;
		}
		$data_tmp = $new;
}
leavewhile:

foreach (sort($new) as $val) {
  echo $val . "\n";
}