Add option for downloading only new items from playlists

I download an ongoing series through a playlist. Since it's ongoing, new items are added to the playlist. Right now it's kind of a pain to download new items from the playlist.

I either have to paste in each new video URL manually from the YouTube playlist, or I have to paste in the playlist URL and then uncheck all the episodes I've alread downloaded.

Would be nice if I could specify a range in the playlist downloader, or if it just look in the target download folder and skip existing episodes (taking the new enumeration into account).

This would make the 4K Video Downloader much less annoying!