Its most likely actual .cue files, or .sacd files, at least for me those always show up again.
I suppose FLACs with embedded cue might also fall in there. All the files which don't actually get imported as-is themself, but cause other entries to show up instead (ie. the elements of the playlist they correspond to).
But no, there is no way to get a list right now.
They might show up in the normal MC log, which is a bit hard too read for non-developers, though.
There isn't really reason to worry either. If it fails to import something, it'll let you know (and/or put the file into the "BAD" database). If it simply decides not to import anything because the content of those "playlists" is already in the database, it'll simply show "0" in the final summary.