Another important part about forward-and-backward-compat is that protos support passing unknown fields. If I add a new field into a shared proto that A, B, and

Another important part about forward-and-backward-compat is that protos support passing unknown fields. If I add a new field into a shared proto that A, B, and C all use if A and C have been updated but B was never updated as long as B uses the proto correctly it will have the new field delivered to C. I use this at my current job where our client is a hardware appliance that we are not at all allowed to update so, if we need to add new data for our backend to handle that the client downloads locally we can and we don't need to worry about pushing new client code to do it. This is magic for anyone who has been using Retrofit or something similar and sees fields dropping as normal.