How do I migrate the "Created" and "Modified" date fields?
Turns out that for created &amp; changed dates, they are stored differently than field_date's, you must convert these to Unix universal time.

  changed:
    plugin: format_date
    source: update
    from_format: 'm/d/Y'
    to_format: 'U'
    from_timezone: 'UTC'
    to_timezone: 'UTC'
  created:
    plugin: format_date
    source: DateCreated
    from_format: 'm/d/Y'
    to_format: 'U'
    from_timezone: 'UTC'
    to_timezone: 'UTC'