Hi,
This worked for me - but make sure you have a back up before attempting!
1. Append all the values in column C to column M.
2. Append all the original values in column M to column C.
3. Use Data-->Remove Duplicates on column C only. This should leave the original numbers in place but leave the missing values from M on the end.
4. Use Data-->Remove Duplicates on column M only. This should leave the original numbers in place but leave the missing values from C on the end.
5. Sort all of Group 1 by column C.
6. Sort all of Group 2 by column M.
7. Check to see if they now line up.