Diacetyl can occur naturally in organic flavors as well as several sweet flavors. I spoke with the owner of perfumers apprentice about it and her reply was, they are not going to test every batch for a substance that is not considered harmful by the CDC, OSHA, NIOSH or the FDA. The links to it being harmful are not based on pure facts, only speculation and there are many other factors that could lead to, or led to cases of Bronchial Obliterins or "Popcorn Lung"
If you read thru the cases, there are many things that are not logical, such as, the people who ended up with the problems, poured 5 gallons buckets of steaming hot pure diacetyl into vats of hot solutions every day, 8 hours shifts for several years. There is a Dr in Greece that is doing research on it, but some of the recommendations are based on the theory of this being a cause, but not based on any factual findings.
None of the agencies banned the product, but did recommend that a substitute be searched for. Some of the replacements are more harmful than the Diacetyl in the first place was even considered to be. But, on a vaping standpoint, the levels of diacetyl are typically less, by far, than you inhaled as a smoker, and they still use it in ciggies now to this date.
I agree that caution should be used and attempt to avoid it, but, it is a naturally occurring substance and will show up in many sweet or fruit flavors as well as custard style flavors randomly.
In the case of these people offering test results, they would need to include batch numbers for each flavoring used in order to present a valid test, but that is also exposing the ingredients to their recipes. They are selling fear only at this point and it is just marketing in my opinion, and I am not an expert on the subject, just someone who tries to look at things logically. I question my doctor when he makes a diagnosis/guess as to how he is going to treat me, and we generally come up with a mutually acceptable resolve and I do not have to make multiple trips to the doctor for the same thing