Where do you draw the OEM line?
I draw it this way: Vortex and many other companies offer both OEM models and models they designed themselves or had the OEM alter to their own specs.
The Euro Big 3 utilize OEMs for their products and/or parts of products themselves, so maybe drawing the line isn't so simple for them, either.
Just a couple examples Vipers and Monarch 7's are different color, Talons and Zen Ray Primes, Zen Ray spotter/Razor HD to start. In all of the Asian import glass, you can find matching optics (weight, dimensions, coatings, body design, etc) and evaluate them side by side with exactly the same results. Hence my branding company remark.
Three misses there, WRO, but it does prove my point. The Vipers and Monarch 7s can't be the same design, because their FOV specs are substantially different. The Talons and Primes are completely different designs, although the Talons and Zen Ray ED series are kissing cousins. The Zen Ray and Razor HD spotters also appear the same externally, but have been internally examined to find they aren't identical either.
Just goes to show there is more to the story than looks alone.