Is a question about an authoritative source on-topic, on cooking.SE?
It seems an off-topic question to me, as cooking.SE is not a site for questions about food tests. Am I being too restrictive?
"Short answer, yes with an if; long answer, no with a but."
There's nothing off-topic about a request for authoritative sources as long as the subject matter is cooking. The trouble is that it should be redundant, in theory. The additional trouble is that it isn't actually redundant, in practice.
Cooking has science and experimental data behind it. Tons of it. It behooves all of our members to cite authoritative sources when they answer non-trivial questions. Anecdotal "evidence" is anything but. Since most of us are not food scientists ourselves, citations are essentially the only way to verify the accuracy of an answer.
The problem is that people don't answer this way. I very, very rarely see citations in answers, even when those answers can be supported (or in some cases, refuted) by scientific evidence. Most people - and I'm not completely immune to this myself - will tend to go for the quick and dirty approach to answers whenever that seems to be the expectation. Going the extra mile is, well, hard.
So essentially what it comes down to is that if you want hard evidence, you have to ask for it. I've done it myself when I've had questions on topics where people tend to be thick on opinions and thin on facts. I see nothing wrong with that approach.
The problem I had with the original question was that it essentially just re-asked a previous question but added in some filter conditions for answers. That kind of duplication is not encouraged. The important issue, and one which the OP thankfully understood, is that questions about authoritative sources have to be testing a specific claim, otherwise they're unanswerable. A broad question like "why do we add salt to pasta water" is clearly not going to have a single authoritative answer, but a specific claim like does salt prevent pasta from sticking is clearly testable, even if it is rather difficult to test thoroughly.
So yes, the questions are on topic, as long as they clearly indicate what sort of evidence they're seeking.