I wrote about “x years on” in 2011, where “x” is a number and the phrase means, roughly, “x years later.” (I say “roughly” because I think “years on” is only used in ongoing contexts, whereas “years later” can be retrospective. You could write, Jimmy Carter was elected president in 1976. Four years later, he was defeated.” But not, “…. Four years on, he was defeated.”) The date of my previous post is significant, since it was prompted by discussions of the 9/11 attacks on their tenth anniversary. A good number of them used the expression, especially in headlines, where the brevity of “on” is a virtue. For example, “10 Years On: Finally, Smarter Airport Security Screening?” (Wall Street Journal). And “Though we’ve felt the impact of 9/11, more will yet unfold. Ten years on, it still might be too soon to tell.” (Sacramento Bee.)
We’ve just experienced the twentieth anniversary of of the U.S. invasion of Iraq and my sense is that “years on” is even more popular in discussions of it. Thus, from Google News, and then the New York Times:
The phrase is hard to research since it’s used in many other contexts, e.g., “She served two years on the president’s staff” or “I’ve spent five years on the problem.” But I can say a few things about it. First, it’s fairly new, and second, it’s British in origin. The first use I’ve been able to find is in a Parliamentary address in 1964: “We are more than ten years on since Aneurin Bevan uttered those words.” Four years later, an Alan Bennett play called “Forty Years On” was produced in the West End. “Ten years on” was said Parliament twice in the ’70s and ten times in the ’80s, some in reference to a book called Ten Years On in Northern Ireland.
Here’s the Ngram Viewer graph for American and British use of “years on”:
There’s a lot of noise in the graph; that is, it includes uses of the phrase in other contexts. But I believe the gap that begins to yawn in the late ’60s represents British adoption of the “X years on” expression. The first American used I’ve been able to find is a headline from 1991: “A Consummate Teacher: Coach Robinson 50 Years On.”
Thirty-two years on, it’s fully arrived.
Update: Reader Ian Christian reports that the Harrow school song, composed in 1872, starts out:
“Forty years on, when afar and asunder
Parted are those who are singing today,…”
So obviously, Bennett’s was referring to the song in the title of his 1968 play. I still have the sense that the “x years on” formulation was rarely used until the 1980s. But I could be wrong.
notoneoffbritishisms.com 
You are certainly right, Ben. This expression has taken over American in the same way that “gone missing” has. It is now pretty standard usage. Unfortunately. There is no advantage to “years on” other than it sounds British, which is, often for Americans, enough reason to use it.
I’ve become so acclimated to it from U.K.-sourced TV that if it appears in U.S. TV or in print I barely notice. I’ll have to start paying more attention.
“Forty Years On” comes from the Harrow school song.
“Forty years on, when afar and asunder
Parted are those who are singing today,…”
Thank you!
And Wikipedia says the song was written in 1872, so not that new.
My suggestion is that ‘on’ implies that whatever it was is still happening or still having an effect; whereas, ‘later’ implies that whatever it was is over, and fully a part of history.
I would agree with this. ‘Jamaican independence – 60 years on’ would be a discussion of what Jamaica is like today after 60 years of independence. ‘Jamaican independence – 60 years later’ would be a discussion of the events of Jamaica’s independence from a 60 year perspective.
Perfect.
Note about the sample sentence: you left out the opening quotation marks. I could easily imagine a 1980 headline: “Carter four years on, will he be defeated?” That seems to match most of the examples you give, but I suppose it qualifies as “ongoing?” His defeat/victory is not, however, ongoing in 1980, only his presidency is.
“We’ve just experienced…”
Isn’t the use of the present perfect tense here a NOOB? 😉