I remember finishing them all except for the very last extra-long-and-hard (hur hur) level. I should probably go back and take that one on again one day, if I managed the equivalent final level in Odyssey (Darker Side of the Moon?) I should probably be able to do this one if I really want to.Yesterday i finished a few levels in SM3D Land, stopped at the end level (Bowser's Lair). Got all the star coins up to that point. I had to look up where some of them were, i tried locating them on my own at first but didn't find those problematic ones..
I see that there're "Special levels" after you finish to the end credits. Will try some of them, i think they're supposed to be a little hard, but i'm up for a decent challenge!