From my understanding, you want to customize the plot such that data other than the legend related to plot should be added to the top left of the plot.
You can use text to add data at a specific datapoint in the figure.
The following example explains how to use text
v = 1:5
lgd = legend('a');
num = 123.45
txt = "Sample Text = " + num
text(1.5, 4.5, txt)
here (1.5, 4.5) specifies the position where the text has to be placed.