I'll add that there are also batch to batch variations in a model of light's performance too. Just as you can buy two of the same sports car, and one will be faster...two of the same light can also be different.
The rule of thumb is that a 15% difference can be expected for most mass produced high output lights, and that when added to the variations in testing, a difference in reviewed specs is expected.
Add in the tester's testing methods having differences in design, calibration and interpretation, and that some over or under represent throwers or flooders, etc...so, the specs of the tested lights will vary, and, the way they are tested will vary, and those variations add up to even larger variations, and so forth.
That's just for lumens for example.
For throw, it gets even more interesting, as different beams require different distances to collimate. There was even a fairly recent example of a MAKER who used a lux meter w/o really knowing how, and published throw specs that were LOWER than the real numbers.
My guess is that many of these guys simply do what the hobbiests do, and publish the results "as per ANSI Specs".
IE: They may not be sending them out to a real ANSI certified lab for testing.
If they guy DOING the testing does a REPRESENTATIVE job of it, his results may agree with our reviewers closely enough for us to say "Those are real numbers".
If the guy fudges or screws up, etc....and the numbers DON'T agree with our reviewer's numbers, we call BS.
In fact, the reviewer's and maker's testers could even be making the same errors, and the "real numbers" could be different yet again, and so forth.
Huge firms like Surefire, with gov contracts, etc...are the most likely to have actually sent products to an ANSI certified lab. This is why early Surefire defenders were apocalyptic over the "Chinese Lumen" claims...as THEIR lumens WERE accurate, and those chinalumens were the opposite of that.
As the Chinese (etc) lights that BECAME quality-conscious, developed, their lumens fell into reality, and, a 500 L Surefire and a 500 L Klarus (for example) both seemed to have 500 L....but the ebay "10 million gagillion lumen single 18650 military tactical party colored search lights" still used whatever lumen number the advertisement seemed to feel like plugging in there.
So, you simply have to keep a supply of salt grains with you at all times.