The legend list may fill the whole plot window as shown below. If this is the case, the curves at the bottom of the list may not be shown.
To show all curves you can do one of the following
• Move the legend list to the bottom or the top of the plot as explained in the section above.
• Increase the plot window by dragging at the window upper or lower limit.
• Go to Plot->Erase Curves… and erase some curves from the legend list.