This question is a joke right?
There is no federal regulation, and keep quiet about it or there will be. There are industry standards. In the US, they are published by ASM (American Society of Metals), ASTM (American Society for Testing Materials), and several others, though they are different publications, they define things the same, with some tolerances. Any basic steel metallurgy book will define these things. To understand what the definitions mean, you have to know enough to understand the observations that lead to the different categories.
My Smith's Engineering Alloys defines stainless as 12% or greater. The reason is this is where experiments show a sharp increase in corrosion resistance in common corrosive conditions. I prefer to think of it as free chromium, since chromium tied up in carbides (or other precipitates) can't act to reduce corrosion. For some stainless steels, 12% isn't enough to show the sharp increase noted above. For others, it is observed below 12% depending on specific characteristics of the steel, such as ultra-low carbon and sulfide inclusion contents.
High carbon steel starts at 0.6% carbon. The reason it's set here is the change in appearance of the martinsite under a microscope. There is a distinct difference at or above 0.6%.
As much as it pains me to say, the common knife steel faqs aren't very good if you want real information on knife steels. It's not their fault. The topic can be very complicated, and people spend their entire lives trying to learn about it, so it simply cannot be condensed down into a 2 page chart and published on the internet or in a knife magazine or knifemaking book. Statements from well known authors can be right or wrong or both, depending on the property, amount of element, and heat treatment. The authors know this I'm sure, but they are writing knifemaking material, not metallurgy textbooks. Ok, maybe some don't know, but I can't tell by reading the charts, books, or articles.
PS: Ordering material and getting that material are 2 different things. That's why steel suppliers test their stuff, and why customers test it again. It's also why my company bought a Positive Material Identification machine. Did you know polished and stacked 316, 304, 321, and Inconel sheets look alike?
) That's called capitalism, pretty soon every plumber worth his salt is using x copper and y galvanized. and if they see Plumber B using the shitty stuff.... it won't last long.