Right now, dossier and lists need to be in the same site. It would be a great improvement and make for easy re-use of content/data, if a dossier could look-up on existing lists ("masterdata"), that lie on another site or even site collection.
The dossiers "Time Sheet" and "To Do List" both have a look-up on the same list "Clients". This list "Clients" is managed/stored centrally in a separate site called "Masterdata". From every site where the dossier "Time Sheet" and/or "To Do List" is used there is a look-up from the dossier on the centrally managed list "Clients" on the site "Masterdata".