I see this is from Nov - 2012, and here I am trying to figure it out as well. iTunes does clobber music files from the hard drive and references to them in the library database without telling you.
Some examples:
DonMcLean's "Greatest Hits - Then and Now". I ripped the whole CD, but now only 'American Pie' is missing. This CD is not for sale in the iTunes store.
Putumayo's "Putumayo Presents: American Blues" ... I bought the CD, ripped it, and now it is gone. American Blues is not sold in the Tunes store but a few others of his 'Putumayo Presents' are.
Dellé's tune 'Pound Power' I think I bought from iTunes Europe, or from some 3rd party source while in Germany. This song is not listed for sale by the artist in the US iTunes store (at least) but there are others from him here.
I did ask them about this one, and this is the reply I got:
Subj: Music I have added to my library disappears, I believe, because it is not offered in your store (e.g. Title 'Pound Power'; fm EU purchase)
Thanks for contacting us. I understand that you're missing ripped songs from your iTunes library. I can relate to your concerns as well, and I know I would want this taken care of right away. Not to worry, this is definitely something I can help you with.
I would like to mention that we don’t have access to the music you’ve ripped from other sources. The iTunes Player can detect music from other sources that’s on your computer, so the songs can be made available in your iTunes library. However, the iTunes program can’t delete content from you hard drive.
That said, the missing songs may still be on your hard disk. To look for them, follow the steps in this article:
https://support.apple.com/HT203167
Please let me know if you require any further assistance. If you do, I would be glad to help. Thank you very much for being part of the Apple family. I hope you have a great day.
I do belive Apple is cuckolding it's consumers and I would appreciate a straight answer from them about how I can keep them away from my lawfully purchased music despite what they think, and their lack of integrity in regards to controlling from whom we purchase music.
Get over yourselves .. .. ..
PS - I use only Apple products (Mac, Airbook, iPad, iPhone)