How do I have numeric User IDs return employee names?

Build a table with two columns. In Column A, put the EE ID, in column B put their name.

In your sheet where you are doing your calculations and have the EE ID, in an adjacent column insert the Vlookup formula to find the EE ID in your table and return the EE name.

Here is the syntax for Vlookup

http://www.techonthenet.com/excel/formulas/vlookup.php

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Use the same principle as in the original posting. Vlookup. In your list of 2000 names, in a new column use the vlookup to determine if the name in that sheet is on the list of 30+ names.