Hello Snoopy, as I already told you here, it's difficult to imagine what you are doing.
Can you post some example code to examine?
Alternatively, if you have used either PlotY or PlotXY with an array of data, GetPlotAttribute with ATTR_NUM_POINTS attribute permits you to retrieve the number of elements in the plot. Next using ATTR_XDATA and ATTR_YDATA atributes you can retrieve the data array directly from the graph.
Can this be of some help to you?