That's a very good paper. I missed out a couple of mechanisms including the most obvious (and the one I hope the get rid of first: "straight shots".
I suspect most of the issues we're talking about are multiple scatter problems and the correct sizing and plcement of baffles.
The test you describe using darkness and a bright light source is the most sensitive test for stray light but you need to calibrate that test with an excellent bin (an alpha bin) to see how well they do.
It is useful for sorting bins into order on how well they deal with stray light. It was a after a test like this that I sent a Vortex Hurricane back as it clearly had stray light problems (you could see them in normal use but the "moon at night" test showed how bad they were compared to some other bins).
I have three very similar binoculars. The Browning 8x32, which my dad actually has now, the Pentax DCF SP 8x32, and the Pentax DCF ED 8x32. Specs are almost identical for all three, and aside from some cosmetics, the only real difference between them is their coatings and the claimed use of some ED glass element in the SP, more in the ED.
That's an unsupported assumption.
They similar in the sense that they have two barrels and are about the same size with the same sized objectives
They almost certainly have different designs of multilayer coatings and phase-compensating coatings but those coatings are similar in more ways than they differ. The real test for AR coating (to differentiate them is to look for direct ghosts (specular reflections between the lens elements) and even that depends a bit on optical design.
They do differ in optical design. Even though you can't see it from the outside.
AFAIK the Browning (Bushnell Legend clone) doesn't have an aspherical elements in the eyepiece but the two Pentax designs do (the SP introduced them, IIRC). So the eyepiece designs are probably different. They may also differ in their overall optical design in some ways: number of groups, number of elements, focuser design, number of elements in objective, eyepiece and focuser. It seems in this case though they have the same number of elements (5) int he same number of groups (3) in the eyepieces.
And they certainly differ in the fine optical design (you can get the similar specs in many different ways). When you put ED glass in a bin you don't just add ED (though I think Swift did in the 820/820ED) but you optimize the whole design to minimize stay color (not just longitudinal CA (objective) and transverse CA (eyepeice) but dispersion in the prism too. That might mean going to a more complex eyepiece design. Pentax design style is rather different from Bushnell design style (in their other bins) especially over field of view and field curvature (a narrow FOV and flat field is what makes a Pentax a Pentax, IMHO). I suspect under the skin you'd see some of that in these superficially similar bins.
And then there's the interior tube design (coating and shaping), eyepiece lens edge blackening, baffling and positioning of field stops which differ in each design and contribute most to controlling off-axis stray light in test you describe.
It's a problem for us "optical hobbyists" that this stuff is not better revealed to use. Bins are unfortunately mostly "black boxes" for us.