Per J443, you are not required to use T as your verification time. If you use some other time you wouldn't expect the arc height value to be the same as the intensity value.
Using the curve you could select a time (after T) and see what the arc height should be for that time. You would then verify intensity by running a strip at your selected time with the goal of getting a "target arc height". If you succeed in doing so, you are verifying the saturation curve is still valid, thus the intensity has not changed.
Using this method you would take the longest T value of your 3 solved curves and find the arc heights for that time on the other 2 curves. This allows you to verify all 3 locations with a single time.
We describe this procedure at our US Workshop and international seminars. Come out and see us at one!