From the administration guide:
• Enabling duplicate file name checking affects only future operations. Enterprise PDM
does not check the vault for existing files with duplicate names.
• Duplicate file name checking is global to all folders and files in the vault. To support
multiple files with the same name in different folders, consider using file templates
to handle unique file naming.
• When enabled, the following operations check for duplicate file names:
• Initial check-in (including undo check-out)
• Recover (from deleted files)
• The duplicate-name setting is ignored for items. Item IDs must always be unique.