It applies to a point light source, which reflected light is not.
That’s why a phtographer can measure light from an illuminated object at any distance. Try for yourself and measure with your phone an illuminated wall. Halve the distance. What are the figures you get?
It applies to an omnidirectional point source. If the point is directional, like single photon, there is no loss of intensity at any distance — that’s just conservation of energy. The correct way to think about the problem is to look at the statistical behavior of single photons. Your emitter sends photons onto some two-dimensional area (hence inverse square distribution), and then each photon is scattered randomly by the surface (unless it is a true reflector), which means it can go in any direction. Each photon’s point of impact thus behaves roughly like an omnidirectional point source, and therefore the number of scattered photons returning to the two-dimensional area of your retina also follows an inverse square law.
Just do the proposed experiment.
Edit: I did 
. Interesting.
If I double my distance from a uniformly illuminated wall, I’m getting 1/4 the intensity from each square inch of wall, but my lens is taking in 4 times the area, so there’s no net effect. That experiment doesn’t tell us anything. Or are you proposing something else?
For large enough distances lasers still follow the square distance law as we still have difraction, so you can’t expect to shine a laser to the Moon and receive it back from a mirror without attenuation. For close enough distances the dispersion is much smaller than the original beam width so the square distance law may be ignored.
One of my viewers suggested I use an eye chart and sit my camera off to the side, then shine a flashlight at it from various distances to measure usable light. My thoughts would be that the camera is then only seeing the light one way and would therefore be brighter and inaccurate, yes? I’d need to take the photo from where I’m shining the flashlight from.
We’re talking about brightness - luminosity.
See:
Camera in manual mode, histogram plots, distance halved.
I see the brightness doesn’t change significantly, no matter the distance.
The JPG already has some processing applied, they only have 256 possible brightness levels so the scale is compressed in a non proportional way (for example 210 may be 4000 and 220 8000), you would need to shoot in RAW if your camera supports it and disable as much processing as possible.
https://www.cambridgeincolour.com/tutorials/gamma-correction.htm
No, it’s not. Be rest assured I know what I’m doing.
Please provide your data if you doubt the results.
Cool — that’s exactly what you’d expect from theory, but it’s always good to have experimental confirmation.
Talk about getting off topic.
Thank you all who are joining the conversation! I’m working on digging into these right now. One thing I want to mention which I pointed out in the OP. Round trip has nothing to do with it in this case because I am not holding the flashlight, I am standing at the reviving end.
It does not matter if you are holding the flashlight, or somebody else.
Murphey’s law still applies. BTW the only person contesting that axiom is the missus.
The question in the OP is more or less like shining on a wall vs. shining on a mirror.
Scattering vs. reflection.
You have assumed that such a thing as “outside the range of the flashlight” exists—it does not and that is a wrong assumption. That is an advertising concept for selling flashlights and bragging.
Photons of light will travel across nearly infinite distances at a somewhat high speed unless interrupted, dispersed, reflected or absorbed by particles or objects in the beam path.
You can prove this to yourself by shining your light toward a corner cube, a retroreflector target used in surveying, in which any light that enters the cube is send back out at the same angle. If you do this you will find that the “range of your flashlight” is much further than advertised.
There is one of these on the moon that can be hit with a laser to measure the distance to the moon and other cool party tricks.