Unwanted hollow star / album ratings foul up a Smart Playlist of zero-star songs

The SXSW Showcasing Artist compilations typically include more than one thousand songs. When I add them to iTunes initially, the songs display a blank rating, which is what I want.

The songs are each tagged with the album SXSW YYYY Showcasing Artists (where YYYY is the year of the festival). They appear in coverflow view as more than one thousand distinct one-song albums, which is unwieldy. So, I gather them with a Smart Playlist, select all, open Get Info, set the album, year, sort album, and mark them "Part of a compilation."

Then I start listening to them, and rating them one to five stars. In some cases, I do not need to listen all the way to the end in order to determine a rating, so the "Played" count does not increment. Sometimes the song plays all the way to the end and I can't rate it because I'm too busy. Sometimes a whole bunch of songs play to the end and I never hear them because the headphones were plugged in to the player but not to my ears. The only way I know I have actually heard enough of a song to be able to rate it is that it has a rating.

Then, something happens. I don't know what.

Some of the songs to which I have never listened show a two hollow star rating. I guess that's the Album Rating. What the heck?

I want a Smart Playlist of the songs I have not rated yet, whether or not they have been played, and I do not want to count "Album Rating" as a rating. I want the zero-star songs, and the Album Rating makes the Smart Playlist think there are no zero-star songs.

I would be delighted to remove the Album Rating, but there appears to be no way to do so within the iTunes GUI.

I do not mind writing a program to remove Album Rating from wherever iTunes stores it, and based on Google searches such a tool would be popular. Is iTunes library format documented? Does iTunes generate Album Rating dynamically, so even if I were able to erase it from the disk, it would come back?

Note: the technique "View in Album List, click to the left of the leftmost star" does not always work. See here and here.