Literature consulted for the Question

It's interesting to look at the stream of materials gathered and consulted as this Question unreeled. The beginning (in early August) was via a Literary Review piece:

"A Camera of One's Own" Miranda Seymour in Literary Review June 2023 (a review of Sarah Knights' Thoroughly Modern: The pioneering life of Barbara Ker-Seymer, photographer, and her brilliant Bohemian friends which I got and read via Kindle, and so (via the Bright Young Things of 1920s London) was reminded of Anthony Powell's A Dance to the Music of Time, described as "brilliant literary comedy as well as a brilliant sketch of the times" ... and thence to Hilary Spurling's Invitation To the Dance: A Handbook to Anthony Powell's A Dance to the Music of Time, an index of the 400+ characters who appear in the 50 years and 12 volumes of Dance). Thus was I reminded of my long-running fascination with cohorts

In the same June Literary Review there's a review by Richard Reeves of Peter Turchin's End Times: Elites, Counter-Elites, and the Path of Political Disintegration, which John-the son had also pointed me to, saying

This seems like a different take on the strauss-howe generational concept, one that theoretically is more data driven and less ... mythological. But given the fabrication of academic data by Honesty Researchers at Harvard and Duke, that makes me wonder how much fraud or just plain affirmation bias is papered over in academia. And once you marry it with the motivations inherent in publication, i get pretty suspicious. Were there corners of academia that gave you any safe harbor from these pernicious forces?
Some of Reeves' review struck several harmonic chords:
Trying to find ourselves in a cyclical historical process is (a) a bit of a balancing act and (b) bounded by not being likely to see this cycle complete... Hegel... argued that societies develop in a series of cycles, each of which is characterized by a certain spirit, or zeitgeist... (Integrative phases are characterized by) internal peace, social stability, and relatively cooperative elites ...also periods where the proceeds of economic growth are reasonably evenly shared. (Disintegrative phases, by contrast, are marked by) social instability, breakdown of cooperation among the elites, and persistent outbreaks of political violence, such as rebellions, revolutions, and civil wars... 'intra-elite competition and conflict' is the single biggest predictor of instability. The condition to watch for here is 'elite overproduction'. This occurs when there are not enough elite roles for the number of people who feel entitled to them. A contemporary example is the gap between the number of college graduates and the number of jobs that actually require a degree...

Mid-August brought Betsy's 80th birthday, and I happened to be reading Moa Petersén's Eighth Day Wonder — Jerry N. Uelsmann, in which she referenced

...the human potential movement and the counterculture movement forming among white, middle-class students at US universities in the mid-60s...
and I thought:
exactly the milieu in which I moved and flourished. The cohort we beloged to is now ... OMG 80!
...So what effects did our cohort have, now that we're beyond any influence on how it's going down? ...which reminds me to read the Harper's piece on Generation X...

And so to Justin EH Smith's My Generation: Anthem for a forgotten cohort

Next was a Medium post by Daniele Nanni: A Glimpse into the Future

The Digital Age revolutionised civilisation by digitising information, encoding words, sounds, images as abstract 0s and 1s independent of physical media.

This let messages transcend distance and time creating the seed for new forms of culture that decentralised communication, democratised creativity, and diversified expression.

Information became portable, shareable, and freed from geographical constraints. In other words, knowledge became more accessible for an exponentially larger number of people.

...Our attention has been commercialised and our personal time disrespected. In the digital economy, our focus has become a commodity to be extracted, monopolised, and sold to the highest bidder.

...In the Digital Age, computers were distinct objects that mediated tasks which we could choose when and for how long to interact with.

As the Digital Age progressed, we started to have less and less choice over our technology interactions.

Connectivity became an assumed constant.

...and that got me thinking about how different cohorts/Generations have experienced this juggernaut, and I wrote this:
The 'digitization of our lives' was an important part of the growing up of those in Generation X — they had in adolescence a succession of DEVICES that eased them into digital life, which most of them have spent their adult lives IN, while Boomers only encountered the digital as adults, from the early 80s...

The next day:

The Birthdays have me thinking about how we structure and experience the passage of time, and particularly how that WE consists of our contemporaries,those who share our points of reference IN time...
...and that got me thinking about George WS Trow (1943-2006); for ME, he's Time and Space, though largely erased from public consciousness. So I got from the library shelves and re-read Within the Context of No Context (1980 in New Yorker; augmented edition 1997) and My Pilgrim's Progress: Media Studies, 1950-1998 (1998).

Each one of these social generations —from the '50s, from the '60s, from the '70s, from the reagan era, from now— thinks of its social aesthetic as definitive. In fact, they are all in a process: encouraged toward, and beyond hubris, by demography...

Of course, there would have been no point in counting everything that was happening in television in December 1955, because in January 1956 a human avatar of unparalleled power named Elvis Presley was going to change the whole thing forever...

The big subject is the history of hyperactivity, the speeding up of things... Every child in America has had these crash-and-burn pathways energized and activated... There is no child born now who has access to television who does not have those hyperactive pathways energized and validated...

...which led me to Ariel Levy's George Trow's Battle With Insanity, from New York Magazine 2007.

At that point I found my way to Jean Twenge's Generations: The Real Differences Between Gen Z, Millennials, Gen X, Boomers, and Silents—and What They Mean for America's Future (2023) via Kindle, and with many additions to the Kindle Notebook...

...and that led me to wonder where I'd first encountered the age cohort idea, and I was reminded of Erik Erikson's Childhood and Society (which I had not read in 1962, when it was assigned in the first Anthro course I took...), and then pointed to The Life Cycle Completed (Extended Version): A Review. So I got them both on Kindle, but found that 'cohort' was not mentioned in either, BUT the paradigm of life stages drew my attention, and led me to

An exploration of Erikson's eight-stage model of development as measured by the Expanded Inventory of Psychosocial Development with particular reference to generativity, the seventh stage. Arianna N. Jarvis, U Mass Masters Thesis (1992)

Connecting Life Span Development with the Sociology of the Life Course: A New Direction Chris Gilleard and Paul Higgs (2015)

The final stage of human development? Erikson's view of integrity and old age Chris Gilleard (2020)

...and THAT all led to the book mentioned by John-the-son, Strauss and Howe's Generations: The History of America's Future, 1584 to 2069, in a new edition published only 4 days ago, 1500 pages and just acquired via Kindle.

William Strauss and Neil Howe posit the history of America as a succession of generational biographies, beginning in 1584 and encompassing everyone through the children of today. Their bold theory is that each generation belongs to one of four types, and that these types repeat sequentially in a fixed pattern. The vision of Generations allows us to plot a recurring cycle in American history--a cycle of spiritual awakenings and secular crises--from the founding colonists through the present day and well into this millennium.
(Amazon blurb)

That's a LOT of territory covered...

And to be truly horrified, read Boomer vs. Silent Generation: How to understand consumer behavior to innovate senior living.

Josh Glenn on Generations and Cuspers (2010)

According to my generational periodization scheme, someone can be born on the cusp between two generations.

Being born on the cusp between two generations might mean identifying with the "right" generation. But it might also mean identifying with the "wrong" one. For example: Oscar Wilde, though born in 1854 and therefore technically a member of the Plutonian Generation, is much easier to identify as a Promethean (1844-53); while Vincent Van Gogh, though born in ’53, is best identified as a Plutonian (1854-63).

A person who identifies with the "wrong" generation, however, sometimes also identifies with aspects of the "right" generation. Such men and women find it nearly impossible to internalize either generation's dominant discourse. Such men and women become alienated, hyper-analytical, obsessive, nostalgic-visionary, and quite often angry-funny social/cultural critics.

"No one is ahead of his time," Gertrude Stein (a cusper, born 1874) writes in "Composition as Explanation," "it is only that the particular variety of creating his time is the one that his contemporaries who also are creating their own time refuse to accept [...] and it is very much too bad, it is so very much more exciting and satisfactory for everybody if one can have contemporaries, if all one's contemporaries could be one’s contemporaries." This is precisely how all cuspers must feel.