Tomorrow

The future begins tomorrow:

Poul Anderson's Brain Wave begins with a contemporary setting, then rapidly moves into an amazing future, unlike any other in fiction;

HG Wells' Time Traveller spends eight days in the far future, then returns to the same day so that, in the evening of that day, he tells his dinner guests that he had travelled into "tomorrow," then "Tomorrow night...";

Wells' Invisible Man thinks that his Reign of Terror is the beginning of the future;

CS Lewis' Introduction to his That Hideous Strength, published in 1945, informs us that the novel is set loosely after the War.

Lewis' first two novels could happen "now" (before and during the War, respectively) because no one knows that Ransom has been to Mars and Venus any more than anyone knew that Cavor and Bedford had been to the Moon or that Bedford had returned alone. However, That Hideous Strength is "day after tomorrow" fiction: everything is the same but one thing will be different. The further future is discussed and decided.

Any contemporary novel could be Volume I of a future history. There will be future events. We are usually not told what they will be. But the author could continue the narrative. One way to do it would be:

to write several novels set here and now;
to write an sf series set several centuries hence, too far ahead to be overtaken by events in our lifetimes;
to have the latter refer back to the former.

Thus:

van Rijn refers to a twentieth or twenty-first century ancestor;
a device used in the Technic History began to be developed in the twentieth century;
somebody think of a better example?