It now appears to me that a file recovery tool like Recuva was used. While only 200 GB remains on a 500 GB drive with 300 GB of used space on it, tools like this can report original file sizes of deleted files even when they are not recoverable due to them being overwritten. If you add up all of those original file sizes, they can exceed the capacity of the drive. Not all of it will be recoverable, though.
It is definitely worth it to see if anything recoverable is in the 200 GB of free space on the disk image. Even file fragments can be important. That's why we need a large number of people contributing to the effort--a manual analysis of the bytes would yield more information than a file recovery tool can provide.
This is a nice update.
It now appears to me that a file recovery tool like Recuva was used. While only 200 GB remains on a 500 GB drive with 300 GB of used space on it, tools like this can report original file sizes of deleted files even when they are not recoverable due to them being overwritten. If you add up all of those original file sizes, they can exceed the capacity of the drive. Not all of it will be recoverable, though.
It is definitely worth it to see if anything recoverable is in the 200 GB of free space on the disk image. Even file fragments can be important. That's why we need a large number of people contributing to the effort--a manual analysis of the bytes would yield more information than a file recovery tool can provide.