Adding to shared album results in duplicating contents.

i created a shared album in cloud drive [macos] to make 1 album of the year, but had too many photos to upload together. after an hour had passed, i selected a new set and tried to add to that album-with the album open- hit the add to album link. i ended up with duplications of photos put in first. Deleted and tried again. Same ?how/ what doing incorrectly? Can i select all i want and although they exceed hourly limit will up load later?