[Some files unrecoverable for no clear reason]

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!

[Some files unrecoverable for no clear reason]

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?