tullik wroteVersion 2.0.0.988 on x64 Windows 7
It appears there is little consistency in the content of ...\Cache\FileCache.dat.
The creation of the FileCache is time limited on directory basis. In other words, the cache creator can analyze any given directory only a certain time, after which it quits and moves on the the next directory. This ensures that it will not take forever to create the FileCache even if you have 1 TB of files in you hard drives.
The effect sounds like it was caused by Windows caching. The first time the FileCache was created, the creation was aborted due to the time limits. But on the second time, the cache creation went further because Windows, in turn, had cached the file system queries and was able to give the data to the FileCache creator faster.
tullik wrote
Question: Is FileCache.dat used for anything besides attempting fix of invalid file references in registry entries?
It is used mainly by the registry error fixing engine, but it is also used for example when attempting to fix broken shortcuts with the Start Menu Tool.