I would say you can split them into individual series, each in its own column, then "show series name" except that Numbers has a glaring bug when trying to make a chart like that. In the screenshot below you can see the overlapping series name labels on each end of the X axis for points that do not actually exist. If there is no first or last point in the series, Numbers will put a data label for it at Y=0. No data point, just the series name label. I reported the bug a while ago and again recently when 11.2 came out with the bug still there. Hopefully it will get fixed.

If it does get fixed and if you need to do a trendline or connecting line, you can include the "Y" column as a series with its label off and put the trendline/lines on it.
It is possible to work around the bug by making fake data points that are off the chart and setting the axis min or max so they do not appear.
