Thanks for looking into this.
By retain I actually mean the storing of the data and the graph display. When I tested that using MQTT.fx I thought it only worked with the ‘retain’ flag set in the MQTT message but I may be wrong.
Using alphanumeric channel names it does work actually i.e. the widget is created and displayed just none of the values are stored. When the widget page is reloaded, all values are blank until the next update arrives.