I have a site that is about 500mb.  I've been using HHTrack for about 2 years
to download it for a specific reason for a client.

The entire time, I use an existing project and its settings, but every week
when I update this existing download, it re-downloads every PDF, every image,
etc and it takes hours to do so.  Seems like it ought to be just downloading
changed or new files.  What am I missing?