Conditional formatting>cell rules>duplicates may not be right for the task

Hi

I have been trying to use conditional formatting>cell rules>duplicates in Excel 2007 to identify corporations that submitted required data for every period in a biennial survey from 1990-2010. As you will note from the attached worksheet, company # 660570 submitted data for each year in the biennial period. I though I could use conditional formatting>cell rules>duplicates to identify all of the corporations that submitted data during the period. However, it appears that duplicates struggles when there are numerous duplicate entries.

I am wondering if I have applied conditional formatting incorrectly or if there is a simpler, faster way of accomplishing the goal.

Thanks for your thoughts and suggestions.

Al