A wraparound narrative segment is often necessary to convey important information in a story. The key is in knowing when and how to use it properly.
Deliberately long books in particular depend upon such passages to keep the story rolling along without losing much forward momentum and not sprawling to twice its already doorstopping length. Though this type of narration is all about telling instead of showing, it’s a good, necessary kind of telling. If every single second in a story were shown in detail, the wordcount could easily balloon way past your intentions.
A prime example of when a wraparound narrative segment might be necessary is in regards to a storyline about a character having a long illness or injury, plus an equally-long recovery period. It’s important to know s/he’s sick or injured, but unless the entire focus of the book is that health crisis, readers probably don’t want to know about every day during this time. Just the most vital incidents will do.
Another example is a long journey. Say your characters are returning home or moving to a new place after a war, graduating from university, or leaving a longtime job. Do we really need to know what happens every single minute of this cross-country road trip or two-week train trek? Again, lots of details are fine if that’s the book’s focus, but there’s no point in spending 35,000 extra words illustrating the journey if the meat of the plot only begins afterwards.
You also might need to quickly catch the reader up on what happened between chapters or sections. E.g., your characters were last seen starting summer vacation at one beach, and now they’re at a private cottage some distance away. Or they were about to set out trick-or-treating, and now they’re coming home with lots of candy. Just a few lines to explain the interim will suffice.
What you don’t want to do is stop the story’s forward momentum to tell the reader exactly what’s happened to every character since we last saw them a few years ago at the end of Part II, Part III, etc. Even worse if you do this long infodump after starting a normal scene and don’t resume it till after the infodump concludes.
Instead, convey the most pertinent tidbits naturally, as part of the overall story. E.g., a matter-of-fact mention that Name is married now and lives somewhere else, or that Name now has a higher military rank. But don’t vomit forth page after page of pointless backstory. If it were that important, you wouldn’t have left a long gap between those parts of the book.
Consider what the point of the overall story is, what’s most vitally important for readers to see depicted actively and in detail vs. merely read a short summary of between major events and scenes. Part of me wishes I could do a complete rewrite of And Jakob Flew the Fiend Away, since it covers a bit over 5.5 years in just 128K words and condenses a lot of chunks of time. Had I written it as an adult novel, it would’ve easily been twice as long, with many more chapters, or longer chapters.
But I have to remember I deliberately wrote it as mature upper YA, and that the focus is on Jakob’s frustration at being kept away from resistance activity, finally making an escape, severely breaking his foot and ankle when he does escape and spending months recovering, joining the partisans, revenging his father’s murder, becoming an official soldier near the end of the war, his unexpected feelings for a mysterious girl, and his struggle to adapt to a world he no longer remembers how to live in.
I never intended it as a paint by numbers Shoah story. If I had, Jaap would’ve remained on that train. So many other memoirs and novels detail the Shoah in The Netherlands, but I was going for a lesser-portrayed angle. Spending 100 more pages on Westerbork or the first year of occupation would’ve dragged the focus away from the theme of resistance, and it’s really not important to detail the entirety of Jakob’s 20 months as a partisan. I carefully chose the episodes I did depict.
In my alternative history, I likewise skimmed over a lot of Aleksey’s time in Paris and the apprenticeship to the throne he gets after returning home. Had I chosen to make each of the four Parts into its own book, I would’ve detailed many more things, but I intended each to be successively longer, all building towards the dramatic climax of Part IV. How would it have advanced the forward momentum if there were 15–20 chapters showing Aleksey researching Russian history and government, doing humanitarian work for the Jewish community, and learning the ins and outs of ruling? I would’ve quickly bored of writing that!
If a book is set over years instead of months, weeks, or days, it would be madness to depict every single event. Always think about which episodes are most important to your main plotlines and advancing character development.