Hello Emmanuel, I did not find unambiguous distinction criteria either, be it in the Handbook or in the 2011 book. My interpretation is that Feedback to a Controller helps the Controller estimate how effective its Control Actions have been. Consequently, a Feedback relation has to provide information that is (or can be) influenced by the Control Actions the Controller sends.
This influence can be direct, in which case we have a classic Controller-Process control loop, or indirect in which case Feedback is sent by an entity that does not directly receive Control Actions from the Controller because it is lower in the control hierarchy.
By contrast, what we named Information Exchange in the tool (and is referred to in different ways in the Handbook AFAIR) represents information that the Controller needs in order to carry out its Responsibilities, but that is independent from the Control Actions it sends.
Consider the manager of a fleet of UAVs whose Control Actions consist in allocating UAVs to the people who supervise and are responsible for missions. In order to avoid sending slightly damaged or underperforming UAVs in unfavorable (e.g., windy) conditions, the fleet manager needs to know 1) the state of the available UAVs, and 2) the weather forecast. The former, which is provided by mission supervisors at the end of each mission, is greatly influenced by former UAV allocation decisions so it would be Feedback. The latter, by contrast, is fully outside the grasp of the fleet manager so it would be Information Exchange.
This is, at least, my interpretation. In any case, don’t worry too much: making the distinction is useful for clarity, but mistakes on that will not prevent you from carrying out the rest of the analysis.
Olivier