You have it pretty much spot on, let me fill in your blanks in reverse order, so as to be in chronological order, and to end with the bit you describe as "awesome".
You were correct not to be surprised; it's Italian and like many English words of Italian origin, relates to music being originally an opera term.
An interesting early use in this regard is from George Grove;s A dictionary of music and musicians:
Scenario, an Italian term, meaning a sketch of the scenes and main points of an opera libretto, drawn up and settled preliminary to filling in the detail.
Interesting, because it shows us that in the 1880s it was being used in English, but still noted as "an Italian term".
Now, you ask:
did it experience another shift of meaning in 1910?
Yes, the cinema! As cinema moved from its early infancy into being a narrative art, it took the term scenario and applied it to what is now called a shooting script.
That sense has now died out because...
So, did "scenario" experience a shift in meaning in 1960?
Yes. As you noted:
it became used to describe nuclear outcomes during the Cold War
More specifically, in the hey-day of the think tank in the aftermath of World War 2, Herman Kahn was working for the RAND Corporation on applying game theory to strategic planning for the potential of conflict between NATO and Warsaw Pact countries with their potential to involve nuclear warfare.
He was heavily involved in producing an approach to thinking about plausible outcomes rather than just those deemed likely, and planning accordingly. His approach involved writing scripts for (so-far) fictional events, as if written by people in the future. Since this was essentially taking the fiction-writer's approach to practical ends, he took the term scenario from the dramatic arts, and so he is considered one of the inventors of scenario planning and almost certainly where it takes its name.
While best known now as one of the inspirations for "Dr. Strangelove" his book Thinking the Unthinkable* had some popular success and was much read by journalists in particular. From this scenario in his specialised use, in which it was essentially a piece of military strategic jargon, moved into the popular culture, and from then became increasingly loose in meaning.
Kahn went on to write crazy predictions of how by the year 2000 we'd have new forms of birth-control, sex-change operations, widespread peaceful use of nuclear power, real-time banking and phones that fitted in our pockets. (Clearly a mad-man).
He'd done his bit for scenario, turning it to a jargon use that mutated into the form we know. Thinking the Unthinkable was published in 1962, which you'll note comes in just before the rise in the graph in google ngram.
*Which amusingly enough cites Red Alert, the novel that Dr. Strangelove was a loose adaptation of. Reading it now it's hard not to picture Dr. Strangelove using Dr. Strangelove references.
Oxford dictionary of Word Origins says that the British slang use of bird to mean a young woman is associated with 1960s and 1970s but as you mentioned also, it dates back to Middle Ages. It also adds that the Virgin Mary could be described in those days as "the blissful bird of grace." The modern use appears to be something of a revival.
OED also mentions that this sense of bird was confused with burde , burd n., originally a distinct word and in modern (revived) use, it is often used familiarly or disparagingly. It lists the first usage in 20th century from 1915 as below:
1915 P. MacGill Amateur Army v. 62 There's another bird there—and cawfee!
We might say that the modern usage is revived by media, especially starting from the below usage of News Chronicle article. [It was a British daily newspaper, later absorbed into the Daily Mail.]
1960 News Chron. 16 Feb. 6 Hundreds more geezers were taking their birds to ‘The Hostage’ and ‘Make me an Offer’.
Here, geezer is a British slang for a young lad, bloke (can be an equivalent of dude in AmE). "The Hostage" and "Make me an Offer" were the famous movies of that time.
Best Answer
Early occurrences of 'sales pitch' and 'making a pitch' in the 1900s
The person who coined of the phrase "sales pitch" is not evident from early written instances of the phrase that a Google Books search finds. But those search results point to a very likely source for the popularization of the phrase: The Billboard magazine. A Google Books search finds 21 instances of "sales pitch" from 1950 and earlier—and 20 of them are from The Billboard. (The only exception to this pattern is from a 1949 issue of Television Magazine.)
The earliest instances are from 1943. From "Gabbers Sell in New Garb: Ether Salesmen Now Part of Over-All Production; Dough for Performance Not Names" in The Billboard (November 20, 1943):
And from "Blues Sales Pitch For Swing Frolics Audience on Job," in The Billboard (December 11, 1943):
The related phrase "making a pitch for X" also appears frequently in The Billboard, too, starting in 1942. From "Sellers of E. T. Programs Report Demand for Shows Point Up Fem Angle; Producers Trim Budgets" in The Billboard (July 4, 1942):
This is among 24 instances of "making a pitch for" that appears in issues of The Billboard from 1950 or earlier. Google Books did not turn up any instance of the phrase "making a pitch for" from a source other than The Billboard until 1957.
Early occurrences of 'making a pitch' and allied formulation in the 1800s
I was quite surprised, however, to find the expression "making a pitch" used in a very similar sense almost a hundred years earlier. From Henry Mayhew, "Of the Street-Sellers of Rings and Sovereigns for Wagers," in London Labour and the London Poor (1851):
The story that the ring sellers told prospective buyers was that two sporting noblemen had wagered with one another about whether a person selected at random (the ring seller) can sell a certain quantity of genuine solid-gold rings within a fixed period of time—an hour, say—for a penny apiece. The idea was that one nobleman had bet the other that most Londoners offered the chance to get something valuable for practically nothing (in the "new lamps for old" tradition) would be so suspicious of the bargain that they would turn it down. In reality, of course, there were no sporting noblemen, and the ring seller had bought the rings (which were imitation gold) himself for sevenpence a dozen. The scam sounds sounds absurdly silly until you consider modern email messages from Nigerian oil ministers seeking help from strangers to keep their money safe while they flee the country.
Mayhew's ring-seller informant remarks,
Elsewhere in the same book, Mayhew explain the meaning of "make a pitch" in the context of pitching coins in the air:
It thus appears that "making a pitch" in the street scam sense may have originated with the coin pitching of "three-up."
However, Mayhew also cites several street merchants he spoke to as using the term "a pitch" to refer to an outdoor stall in a fixed locality where items such as fruit or meat are sold, and hence to such street businesses themselves. In this case, pitch may have come from the notion of pitching (that is, setting up) the stall prior to the day's work (as we sometimes speak of "pitching a tent" today). And once pitch is associated with stall sellers, it isn't much of a stretch to imagine people linking the sellers' attempts to hawk their wares with the idea of "pitching."
Yet another complication involves use of the phrase "make a pitch" in the sense of a hawk swooping down to attack its prey. From William Bingley, Animal Biography, Or, Authentic Anecdotes of the Lives, Manners, and Economy of the Animal Creation, volume 1 (1803):
Conclusions
The gap in written instances of "making a pitch" between Henry Mayhew in 1851 and The Billboard magazine in 1942 is puzzling, especially since the notion of crying up one's wares seems to be a common theme of the usage in both instances.
Christine Ammer, The American Heritage Dictionary of Idioms, second edition (2013) traces "make a pitch for" to the late 1800s but doesn't acknowledge the absence of written examples of the phrase during the first four decades of the twentieth century:
J.S. Farmer & W.E. Henley, Slang & Its Analogues, volume 5 (1902) has this entry for pitch:
Farmer & Henley identify several additional instances of pitch in these senses from the later 1800s, but most of them seem to have come from UK sources.
Despite considerable searching, I haven't been able to identify a clear and continuous path in the usage of "making a pitch" between London in 1851 and the United States in the early 1940s, though some such connection seems reasonable enough. In any case, during the 1940s in the United States, "sales pitch" and "making a pitch" were used multiple times to describe promotional efforts on behalf of various appeals to potential customers, and the entity responsible for popularizing both phrases was The Billboard magazine.