tl;dr: This is old news; temper your expectations.
If the reader knows this is old news, then they wouldn't have expectations to be tempered, because it's old news to them.
But if the reader didn't know about it, and finds the news exciting, then it's news to them, why temper their expectations?
There's no logical scenario under which someone would find this event notable, but be bummed out because it happened 9 months ago.
Furthermore, my logic is perfectly valid. Scientific research is time-sensitive by nature. If someone were to post an article hailing the discovery of Neptune, while interesting to someone who has been wholly ignorant of Neptune their entire life, it warrants a caveat noting that it's an outdated discovery. And yet under your logic, you would reply: "There's no logical scenario under which someone would find this event notable, but be bummed out because it happened 168 years ago."