A server is allowed to return a relative to the request URL in the Location header in the response. In a batch request, a request URL can contain a content-ID reference, like $1/Orders to create an order to a not yet created customer. The server can return a Location header of ../Orders(2020) in the response. For the client to be able to determine the correct location of the new Order it MUST perform the content-ID replacement in the request URL (because $1 is not necessarily a single path segment).
We should clarify this by explicitly stating that these steps are required by clients under these circumstances.