I encountered such a problem while using OSRM: I have an OSRM cluster behind a load balancer that processes a continuous stream of requests. To update the road graph, I'm restarting servers one by one. At some point, several servers running with the old graph and some servers with the new one. As far as I understand, there is no way to find out on which version of the graph it was created from the OSRM answer. I suggest to add such field into the response. This can be a data timestamp from the pbf file, or the value of some parameter passed on the stage of osrm-extract.