On top of the Grafana dashboard for the Prometheus Exporter, there are some drop downs intended to filter the graphs. Only the zk_host and base_url dropdowns seem to work. For the collection, shard, replicas and core, they only list "All" value.
Investigation showed that the dashboard was never really completed. Grafana template variable definitions were mostly wrong (using = instead of =~), and lots of core graph definitions only filtered on base_url, not all the others.