Discarding duplicates while downloading
Do not choose this option. Remove duplicates afterwards so you can check if they are real duplicates.
Duplicates removal after import
The searching for duplicates method is safest, but requires much more work.
Method: Top bar > references > find duplicates. Each duplicate will be presented in a window. You can judge whether it is a true duplicate record or not. Sometimes references from the same article differ in how they are presented. Sometimes they are incomplete. In that case always keep the more complete reference.
Are you conducting a Systematic Review? Read this manual for more guidelines: