I agree with Robert. All ID's in backzone need to be in some regular file. The simplest and most compatible way to do that is to put it into backward, and then simply add to the documentation that backward also contains some other IDs from backzone.
One could make a separate file 'addzone', but for some period of time implementations will fail to look at that file, leading to continued incompatibilities. So the better choice is just to broaden the scope of 'backward' slightly.
