The Global Catalogue will allow you to select from different "merge by" options. These options will allow you do things like add a copy to an existing record or create a duplicate record.
1. Click -> Catalogue -> Global Catalogue.
2. From the Tool bar located at the bottom of your screen. Look for the Manage Duplicates by: drop down.
3. Append copy will always be the default selection. But if you wish to change it simply click on the icon and select from the following:
|Append Copy||Adds a new copy if the record already exists in the catalogue.|
|Replace Record||Completely replaces and existing record if it exists.|
|Duplicate Record||Creates a Duplicate Title record and adds a copy to it.|
|Replace on Order||Replaces any records as On Order and sets it to available.|
4. Once you have selected the "merge by" option, You can continue the import process.