How do you know those glasses on the counter touting 8 layers actually has those 8 layers?
It kind of sounds like all you can really do is see if the glasses have the features you requested. Do they transition? Does it seem like they transition as much as you were wanting? Do they seem like they don't have bad glare? Does it attenuate the glare as much as you were wanting? If not, then return them. This is entirely possible with online glasses retailers, they usually have decently generous return policies.
People don't buy glasses because they have 8 layers instead of 7. They buy them because those layers give additional features and it's the features they want. If they can do the features you want in 7 layers instead of 8, does it really matter if it's only 7 layers?
For mid range to high end lenses it would probably be impossible to confirm the actual layer count without destructive testing.
Of course it would be reputation and gut-feel-perception based for most buyers in any case.
However, for the higher end stuff, gut-feel-perception probably wouldn’t be able to tell the difference. Human eyes can’t perceive the strength of lamination between layers, for example.
So it would be entirely reputation based at the higher end.
Which probably explains why high end glasses are vastly more expensive then Warby Parker and other discount places…
In a store you can compare things side by side. If you order something, you get what you get and have no frame of reference.
You can wet them, shine a flashlight, put them under the sun for transition lenses, etc...
Not foolproof, but it would make it harder to substitute the lower end lenses, 3 coatings vs 2 coating would likely be noticeable.
8 coatings vs 7 coatings might not be.
So for the mid range and above it probably doesn't make sense to discount shop at all. Your entirely trusting the brand reputation or shop reputation on whether they will deliver.