In addition, some form corruption is expected to happen due to factors besides the backup software, such as bugs in the kernel or hardware errors. What I wonde

In addition, some form corruption is expected to happen due to factors besides the backup software, such as bugs in the kernel or hardware errors. What I wonder more is why the corruption of the file data wasn't caught by the backup software since it uses checksums for deduplication. A third option is user error such as that between the (user) checksums and the backup there were changes to some files.