Are duplicate photos automatically resolved in the iCloud Photo Library?

I have changed by System Photo Library. After I designated the new library as the System Photo Library and re-enabled iCloud, Photos has started uploading all my photos to the iCloud Photo Library (again).

I don't wish to exceed the storage limit of my iCloud plan, but essentially the new System Photo Library is a duplicate of the previous one, but it now resides on a different drive.

In the process of merging photos from my newly designated System Photo Library with those in the existing iCloud Photo Library, will duplicates be automatically resolved? Or do I need to manually delete the duplicates somehow?