That was close to my thought. Unless you have a good understanding of what you are doing, even using a very basic product like Access to produce a database isn't very easy to do. probably impossible for somebody with no IT training. I would expect that Excel or similar was used.
Even deleted files can be recovered in part or in full unless intentionally overwritten. Files can be recovered from the recycle bin or even from unallocated space by searching on file headers and footers (file signatures. Fragments can be recovered by doing text searches on unallocated space and Excel files have signatures for different sheets, so they can be detected as well.
Unless the files themselves are physically overwritten, it is fairly common to recover fragments at the very least.
Windows also keeps shadow files from restore points and earlier copies of files can be recovered from those artefacts and they are also not easily visible to the average user.
Then there are backups that contain earlier copies of files.
I'd love to know what was found on the various computers and backups. Considering the time it can take to do a thorough analysis, some of this material may not have been available when the interim report was finished.
I was reading a letter from the afl to Asada this morning...one of the attachments from the court case and Minter Ellison set up a virtual data room for remote access to all parties containing all the information discovered by the afl in the investigation. Seemed to be a hosted service by Ansarada.
Would be some juicy reading in there.
http://www.ansarada.com