There's been some disagreement on the topicality of "Where do Feynman Diagrams Appear for the first time?", so I wanted to bring the issue to meta to get input from the community. It could be considered a historical question, which speaks to it being off topic, but it's also asking for the work which introduced a specific notation, which is (at least quite close to) what the specific-reference was created for, and I would say that speaks to it being on topic. What does the community think about this question and others like it which ask for the first work to use a certain kind of notation? Should such questions be on topic?
To guide the discussion, here are three possible outcomes I anticipate (but other options are certainly welcome):
We could decide that questions of the form "What was the first paper/book/etc. to use [notation]?" are, in general, on topic (and should be tagged specific-reference).
We could decide that questions of the form "What was the first paper/book/etc. to use [notation]?" are off topic, but questions of the form "What paper announced the discovery of [phenomenon]?" remain on topic (and should be tagged specific-reference).
Diverging somewhat from the main question, we could decide to make all questions of the form "What was the first paper/book/etc. to [do X]?" for any X off topic. That would be a change in the scope of the site - basically we'd be rendering the primary use of specific-reference obsolete.
It's a fine line, but I think the request for a paper which first uses a certain notation is pretty much exactly what the specific-reference tag was for, so I think it'd be kind of inconsistent to make it off-topic but a specific discovery on-topic.
Completely removing specific-reference as an on-topic subject also doesn't make much sense to me. A final note - this sort of question might be one on topic on both History of Science/Mathematics and here, which isn't necessarily a bad thing.