When you bring new cows into your herd their Visual ID tags may be duplicated by cows you already have. The duplicate VIDs will not display on the in-shed display as every cow has a unique record matched to her EID, Birth ID and VID numbers. Cows with duplicate VIDs must be retagged with new numbers as soon as possible and your Tagging Worksheet updated. This is best done before the milking season starts.
Please note: It is important to Remove Cows you no longer have on your farm. This will stop a major cause of duplicates. See:
How to Remove Cows
Easily updating VID's
Advanced Finding and Fixing Duplicate VID's