Just what whomever was running the testing grabbed I guess, mostly it's stuff just laying around, but can include kits bought for the purpose or even donated or prototypes. There's no real rhyme or reason to it, and what sucks tge most is the sticks not on the list, you've got no clue if they were tested and failed or just weren't tested.
If you figure just in the Trident Z modules, there's 6 colors and rgb, all have different model numbers. 12 or so different speeds, 4 kit sizes, 4 stick sizes, 4 Cas per speed etc, just in 1 model line there's 4600 or so individual model numbers, multiply that by the snipers, RipJaws, Aegis, value lines and a QVL including all of just gskill would be staggering. Then multiply that by all of Corsair, Adata, Patriot, Kingston, Crucial, and all the others and testing all that on every mobo by just 1 vendor would be a bankruptcy in the making.
So they grab 2 here, 3 there, few different sizes and speeds and call it a day, it works with popular ram, here's proof.
And then turn around and tell you that because they didn't test a particular model number, they can't help with issues, but won't tell you that the blue heatsink ram is identical to the red heatsink ram except that changes nothing but the color of the heatsink, therefore the model number.
That was about 20 years ago on an MSI mobo, with gskill ram. Called gskill, sent them a copy of MSI response, gskill mailed me a brand new set of the blue heatsink that was on the QVL with a number to call direct to a gskill rep and a note saying call that if there was any further issues and gskill would handle it from there.
Kingston, Crucial, Gskill, Patriot, Corsair. That's all I will use.