You can add new data series one by one with the chart right click menu. (Not very comfortable.) It is also possible to add additional data series in a chart with drag&drop, holding [Ctrl] key. But that is not obvious (there is no such menu command in LO) and does not work if the chart is not on the same sheet as the data table. So it would be really helpful, if new data series could also be added to a chart with Copy and Paste / Paste special like in Excel. (In LO in the moment Paste inserts the copied cells in the chart as a picture like a screenshot!)
Valid enhancement
Bug is still present. No changes in bug behavior. Testsystem: LO 5.2.3.3 on Windows Vista