When you upload a playlist a second time, MC will skip tracks that have already been uploaded.
A quick question on a slightly related topic...
Sometimes, the playlists i have created will have the same song on one or two or three playlists.
Does that work with CloudPlay, i.e., can I have the same song on multiple playlists?
btw, I uploaded my first playlist yesterday, an assortment of some vinyl that I had digitized over the years. The upload process went quite smoothly (kudos!), though I would have liked a faster upload speed from my ISP for that 500MB Pink Floyd tune.