Every writer who begins writing about characters who will appear in a series of stories eventually has to make some decisions. Among them are: Will my characters age in the course of their adventures? Will the world around them change or are they permanently in the period in which they began? Every author--no matter what the genre--answers those questions differently.
Arthur Conan Doyle--although he wrote the tales of Sherlock Holmes and John Watson over a period of some 40 years, from 1887 to 1927, he largely kept their activities in the period before World War One...and, except for the idea of Holmes' retirement in His Last Bow, they remain essentially ageless.
Another famed detective team, Nero Wolfe and Archie Goodwin (created by Rex Stout), are treated somewhat differently. Their adventures span about the same amount of time, from 1934 to 1975, and like Holmes and Watson, they remain the same ages throughout. (There are minor hints that they have aged somewhat, perhaps five years or so, in that span.) But Wolfe and Goodwin's world advances just as the real world did in those four decades. Cars become sportier and faster, New York's skyline changes, television replaces radio, the Mets replaces the Giants as Archie's favorite team.
Erle Stanley Gardner took the same tack with Perry Mason. Mason remains a man in his prime through pretty much the same period as Wolfe and Goodwin, and his world is always contemporary with the period in which the stories were published.
Yet another team, Modesty Blaise and Willie Garvin, began their adventures in a comic strip in 1963 and continued there and in a series of novel and short stories from 1965 to 1996 (the comic strip continued until 2000). Peter O'Donnell keeps them essentially the same age throughout and the world around them reflects the period the stories were written.
This creates interesting problems for two of these series--the Wolfe and Blaise stories. Perry Mason's "origins" are not specifically tied to any one era or event (despite what the current TV series says). Thus nothing prevents him from having been born at the turn of the 20th Century (as he must have been in his earliest stories) or around World War 2, as the last of his stories would imply.
But Wolfe is established as having been a "freedom fighter" in his native Montenegro--at first in the period before the first World War, when the Balkans were a hot bed of various failed revolutions. Wolfe is said to be in his late teens and early 20s at that time and, as he is generally assumed to be about 50 during his career in New York, those events must have occurred around 1900. But if he is still about 50 years old in 1970, and he was 20 when he was a "freedom fighter," those events would have happened during World War 2.
And now, we have a paradox--Wolfe and Goodwin were both working for the US government during WW2, Wolfe as a special adviser, Goodwin as a major in the Army. Those events are frequently referenced in stories that take place after the war, even up to the 1970s.
A similar situation faces us when tracing the origins and career of Modesty Blaise. We're told she was a "displaced person" in the Middle East when she was, perhaps 10-12 years old. As she is in her early 20s in 1963, that would put her "origin" at about 1950, and her circumstances a result of either WW2 or the creation of Israel in 1948--possibly a little of both. But she is still in her early 20s in the 1990s...so what caused her to be a "displaced person" about 15 years before that? Well, the Yom Kippur War was in 1973, perhaps that is the catalyst. And any of the number of other conflicts between Arabs and Israelis between 1948 and the present could explain her beginnings now.
In another posting, I'll deal with problems facing characters such as Superman and Batman.