Though I’m not sure if I’ve been lulled into a fall sense of security by finding the date on the cover sheet of the PDF (prepended by the article’s publisher/distributer, I imagine).
In no way am I disagreeing with you, more sharing the fact that I’d be surprised and frustrated to come across this omission. Author and publishing date are arguably more important than the title, in my opinion - which now that I think about it is probably why these are the metadata we use to index citations.
Here's an almost completely random example, I literally searched for "graph coloring paper" just because that was a subject I could think of top of my head, and found this as first hit: https://www.cs.cmu.edu/~avrim/Papers/coloring_worstcase.pdf
Yep, no date.
I work with papers in CS/math and have been able to find dates and metadata like DOI pretty quick. There are complications when there are really multiple versions of a paper, like one in a conference that is only an extended abstract and one in a journal, but you would need to figure out which version you want to read in that situation anyway. I agree it's annoying, but coupled with reference manager software like Zotero it's hardly an issue for me.
Great, so I guess I at least know that it must not have been published before 1989... (before I just search for the title on the web, in the hopes of finding a journal it was published in).
Then I went back to this particular PDF and notice that indeed, it doesn't have the date of publication.
Then I re-read your sentence.
"I think the most annoying omission from the standard academic paper format is the year of publication." is subtly ambiguous.
"Sometimes authors omit elements required by the standard academic paper format, and of those omissions, omitting the date of publication is the most annoying."
I assume that's because those papers are, well, published, and of course there's a date on the journal itself? Doesn't really work that way nowadays anymore.
And in fact, most/all CS papers _do_ have a "real" version _somewhere_ that has the date and other relevant info, but in CS, we have a bad habit of passing around links to a papers that point to a random version that the author posted somewhere, rather than to an entry in a proper bibliographic database or to the canonical/archival PDF of the paper. I.e., not the PDF that the author posted themselves somewhere (likely missing dates, publication information, revision history, etc.), but the version that came as part of the conference proceedings or journal that the paper was published in. Those typically (though admittedly not always, depending on the conference) have headers/footers added that include whatever would be needed to properly cite the paper. Google Scholar etc. try their best to link to the "right" place, but are often led astray and point at the "random early draft on the author's website" instead, which of course perpetuates the problem.
Incidentally, helping avoid this situation is the sort of thing is at least nominally a big part of the "value add" that traditional journal publishers are supposed to be adding- keeping track of citation/bibliographic metadata, assigning and managing DOIs, ensuring that there's a standardized layout and production process that includes such information in PDFs, providing archival/canonical URLs for papers, etc. It's also an important part of what professional societies that have publishing arms (ACM, IEEE) and libraries (like the NLM and its PubMed/MEDLINE services) contribute.