Profile0 is a plot of the grating shape: the refractive index variation with Z over one grating period. That explains why 0 < z < .5338 for that plot. OptiGrating will display that curve in its own interface if you right click on the Profile tab and select Shape…
Plots 1, 2, and 3 display local period, apodization, and average refractive index. Those are defined over the length of the grating, 0 < z < 50,000. The number of points for display comes from the number of segments specified in the Grating Definition dialog box. The file will show the value at the beginning and the end of each segment: two values per segment. Therefore if there are 100 segments, there will be 200 points.