Sorry, pl disregard this earlier sample as I forgot to adapt the range
in col C's array formula to suit the actual extent of your sample data

My suggestion as applied to your sample is available he
http://www.flypicture.com/download/MzcyODY=
Madenning_Dilemma2_1.xls


Here's the corrected sample:
http://www.flypicture.com/download/MzczMDU=
Madenning_Dilemma2_2.xls

The array formula in the top cell C1 should be:
=IF(B1="","",IF(ISNUMBER(MATCH(-A1&"_"&B1,$A$1:$A$2197&"_"&$B$1:$B$2197,0)),"",ROW ()))

since your data was down to that row, 2197

No change to the formulas in B1 and E1.
All formulas in B1:C1, and in E1 to be copied down to row2197
--
Max
Singapore
http://savefile.com/projects/236895
xdemechanik
---