Hi,
You should be able to plot as many XY arrays to the graph as you need. As long as you don't delete the previous plots they should remain there. This will make things much easier than dealing with 2 graphs.
There is an example at "C:\Program Files\National Instruments\CVI70\samples\userint\graphlegend.cws" that you can look at for an application with multiple plots.
I hope this helps.
Regards,
Juan Carlos