Spotlight does not store every single quick blocks in the playback database in order to avoid consuming too much storage for data. Spotlight will need draw the graph from information stored in the playback database when you first launch Spotlight client. So there is a possibility, if the Spotlight client is closed and re-open it, you won't have the same graph prior to re-starting the Spotlight client because Spotlight will not necessarily have stored some fast blocks.
If there are two clients and one of the two clients is started at some time when the other client has already been running for long period, the graphs of the two clients may not completely match until both of the clients have ran enough for their graph data to be filled with real time data.
