Some files unrecoverable for no clear reason

[daveybops]

Today, I made the huge mistake of deleting in one go, about 1.8TB of data, filesize averaging 2GB

I realised my mistake immediately, and stopped using the drive.  I downloaded recuva and installed to other drive.

I scanned and about 15% of files are unrecoverable, with comment "File's data could not be found on the disk" when I know the files data was there 10 minutes ago.

Deep scan gave same result.

Other undelete programs could not recover the files either.

Could anybody suggest why a random selection of files were unrecoverable - where they fragmented before deletion?  And can I possibly get my files back?

[Augeas]

This message usually comes up when the deleted file is large, in excess of 4gb. When files of that size are deleted NTFS zaps the cluster addresses, so the data can't be found.

Although the data may still exist on the disk it will be extremely difficult to recover. A deep scan should find the first extent, under a generated numerical name, but the other extents can't be identified without professional help.

[daveybops]

8 hours ago, Augeas said:

 ....but the other extents can't be identified without professional help.

Or expensive software, as my own research suggests.

Many thanks for the advice though!