It is not generally meaningful for client drivers to attach a readConcern argument to getMore commands. The purpose of readConcern is to set the isolation and consistency behavior for a newly issued query, and the purpose of getMore is to fetch a batch of documents from a cursor established by a previously issued query. Furthermore, the getMore command is an implementation detail of the driver and servers, rather than an interface presented to client applications. As such, mongodb servers must either ignore readConcern on getMore commands or reject getMore commands with readConcern arguments as malformed when such commands come from external clients.

Returning an error is less subject to misinterpretation by driver authors, and so is the suggested approach.