I saw your other thread here http://www.gnutellaforums.com/showthread.php?t=61691

I can think of a couple of reasons.
1. The incomplete files were ones selected from fake sources; Recognising fake files

2. Your incompletes are from a much older version & have been incomplete for a long time. The newer version might struggle to know how to connect them. Searching individually for the sources in specific searches might be the best way.

3. From the previous point about much older incompletes, perhaps the exact same files with identical hash are not being hosted by the same people anymore or those people are no longer online with gnutella.

4. The incompletes are missing their original download.dat preferences. At some point this file was thrown away.