Q: What happens if you upload via the upload button in iCloud.com while the initial synch from Mac is happening? It is much faster but will it result in duplicate photos?

WWhat happens if you upload via the upload button in iCloud.com while the initial upload via photos app on the Mac is happening? Will it result in duplicate photos?

Also if I haven't removed photos from the camera roll on the iPhone but they are on my Mac already, will this result in duplicate photos when I turn on iCloud Photo Library on the phone?