The theory is that each user should only ever see the message once; as it says, "If you have uploaded other media, please check that you have specified their source and copyright tagged them, too.". After all, every image whose description you don't fix up is more work that you're making for other people.  
Yes, but in reality I do not have a way to keep track of all images I uploaded. I wasn't in the know of the image tagging on my earlier days on wiki. You know how it goes...
If you have the time, can you please review every image I uploaded (as you are perhaps using a bot) and find the images I forgot to tag. There shouldn't be many. 
Talk|@