This is pretty much true when buying Cert-ed Material. But when buying Non-Cert-ed Material things sometimes fall apart. It depends on the Supplier.
The problem lies in that there is No Clear Definition as to what "Stainless Steel" is.
It used to be that people would Not call an Alloy "Stainless" unless it had at lest 15% Chromium and 5% Nickel. Today, it seems that Anything goes.
I have seen people refer to 4130 as "Stainless Steel". I cringe when I see stuff like this. But there Isn't any Stainless Steel police out there enforcing what someone Can or Can't call something as "Stainless".
That was exactly my point. It really depends. I assumed when I said '304 is 304' implied it was in fact 304 (certified). I wouldn't go off a label if I didn't know the companies reputation & like I originally said things labeled just as 'stainless' are a crapshoot in the first place. I certainly wouldn't trust it to be stainless at all. The vendor that I bought mine through is an industry specific vendor buying from an industry specific source - certified & reliable.