I looked at a playlist just to see. I know there is a logic to matching and it takes it in an order.
Ones, that didn't match that I have in my library included the following:
One parameter seemed to be the date/year more than the album, as I had some matched that were on different albums. However, in my library I use the date of release for songs and not the date of the album which will be different on compilation albums (ie. Greatest Hits, Box Sets, Best of, etc.). This appears to be a stumbling block to matching as it is now.
It could also be duration, as this is sometimes off as much as 5 seconds for the same song. Maybe that's out of the parameter they are using, though it seems to be a small difference.
I had two where no album was listed in the downloaded playlist, so they could not be played.
I use semi-colons between artists when there are collaborations and it looks like Dr. Who can't match these either when only one of the artists is listed in the playlist.
It seems they should widen the parameters in the above mentioned instances.
The blank file types were all unmatched tracks, which would make sense, as Dr. Who can't give you what you don't have.
Does this jibe with what you see?