Where do the numbers come from?
 

Some downloaded files are given a five-digit number in the name, as in "Pachelbel Canon, Baro#628C6.mp3" (these appear to be hex numbers, note the 'C')

The numbers are in ascending if not sequential order, which means the name is locally assigned and does not exist in the original. Is LimeWire generating these numbers? Why?

This is part of the resume feature of LW. They are saved under these temporary file names until the download is completed, at which time, the download is moved from the Incomplete folder to the Shared directory and given it's rightful name back. If LimeWire saves your completed downloads with this naming scheme, you can safely rename them. To explain what the meaning of the numbers and letters are, go the the General Usage section of the FAQ. Question 6-4.

:-)