This article explains how delta pass works during a File Migration
The Cloudiway File migration tool allows unlimited delta passes up to 90 days from the initial migration. Each pass is considered a delta pass.
During a delta pass, the Cloudiway platform checks if a file has already been migrated. If it has, it compares the migration timestamp against the file’s last save time stamp, and if the file’s timestamp is more recent, it remigrates the file.
Delta passes do not migrate new or modified permissions on Files. The permissions are migrated when migrating the File.