Note: 
You'll find further information about how to recover deleted data under following link:
Recovering deleted data

Nero BackItUp is a consumer oriented solution and doesn’t utilize the typical incremental or differential backup strategies know from enterprise solutions. Instead there are two backup modes:

Local copy / Online copy doesn’t apply any file versioning, each file only exists once in a backup set so the backup can be browsed in Windows File Explorer easily

  • Unchanged files that have been backed up before won’t be backed up again
  • A file deleted from the source data won’t be deleted in the backup set
  • A file modified in the source data will overwrite the file in the backup set on next backup
  • A file renamed in the source data will be added like a new file to the backup set
  • A files added to the source data will be added to the backup set
  • Not available for optical discs

Local snapshot applies a similar concept but saves new/modified files into new backup sets, so to find different versions of a single file is not so easy

  • Unchanged files that have been backed up before won’t be backed up again
  • A file deleted from the source data won’t be deleted in the previous backup set
  • A file modified in the source data will be available in the next backup set
  • A file renamed in the source data will be added like a new file to the next backup set
  • A files added to the source data will be available in the next backup set

Local snapshots on optical discs are always a full backup every time the job is run.