Excel Validation: How to prevent duplicate entries globally within workbook?

[Kclynn]

How do I use data validation to prevent duplicate entries across multiple worksheets?

 

[Jeffrey Mahoney]

Your data validation list would have to contain all the entries the user's have made. So, you need all entries stored in one main list. After each new entry is made on each sheet, a macro would have to copy that to the main list so that it can be checked for duplicates.