(1) For some of my ripped albums, the cover art directory is missing from the exported XML. I believe that these are files that were place directly in the album drectory and then added with the image "Add from file" action:
<Item>
<Field Name="Filename">C:\Media\Music\Come Away With Me\01 - Don't Know Why.wav</Field>
<Field Name="Artist">Norah Jones</Field>
<Field Name="Album">Come Away With Me</Field>
<Field Name="Name">Don't Know Why</Field>
<Field Name="File Type">wav</Field>
<Field Name="Genre">Jazz</Field>
<Field Name="Date">37257</Field>
<Field Name="Bitrate">1411</Field>
<Field Name="Image File">Folder.jpg</Field>
<Field Name="Media Type">Audio</Field>
<Field Name="File Size">32838668</Field>
<Field Name="Duration">186</Field>
<Field Name="Track #">1</Field>
<Field Name="Date Created">1124720441</Field>
<Field Name="Date Modified">1124720488</Field>
<Field Name="Date Imported">1124720488</Field>
<Field Name="Replay Gain">-14.27657</Field>
<Field Name="Peak Level">0.98746</Field>
<Field Name="Intensity">1</Field>
<Field Name="BPM">89</Field>
<Field Name="Album Gain">-11.400059291294642</Field>
<Field Name="Complete Album">1</Field>
<Field Name="Sample Rate">44100</Field>
<Field Name="Channels">2</Field>
<Field Name="Bit Depth">16</Field>
</Item>
(2) For same albums, the "Genre" tag is missing for all tracks in the XML export, yet looking at the album information, the genre is filled in. I don't have a pattern for this.