I have the same question. I ordered some from Amazon for my kids. I hope this article means that they were carefully verified by Amazon, but it has still made me uneasy about using them. Just knowing fakes are common is really concerning.
It's weird but I've got a co-worker who bought some cheap Chinese ones and actually block more light from a phone's flash LED than my legit, approved pair. I'd still never use them since my test is very simple and I don't understand enough about the properties that make for good solar filters.
If your understanding were correct, the difference between fake and real glasses wouldn't be minor ones such as round-ness of certain parts.