PLAN-LES-OUATES, Switzerland — Thierry and Sandrine Stern have a big year ahead. The couple — president and head of creation, respectively, at Patek Philippe — may have celebrated the watchmaker’s 175th anniversary two years ago, but 2016 looks set to be another landmark.

It’s the 40th anniversary of its sporty Nautilus, among the house’s more sought-after designs, and the 20th of its now-patented annual calendar mechanism. It’s also the 20th anniversary of its much-lauded tagline: “You never actually own a Patek Philippe. You merely look after it for the next generation.”

It’s fair to speculate that the house will mark these milestones with commemorative watches — as it did for the 175th — but Mr. Stern was being tight-lipped during a recent interview. “My press department is getting more tough,” he said with a smile. “‘We don’t say anything before Basel!’ they tell me.”

The last family-owned independent Geneva watchmaker, the company is known for being guarded. “Independence is the key to our future success,” said Mr. Stern, who took over the top job from his father, Philippe, in 2009.

He was speaking in Plan-les-Ouates, home of the company’s manufacturing facility and administrative headquarters for its 2,000 employees worldwide. The offices are airy and contemporary — and in the distance, through panes of glass, one can see the golden façade of Château Blanc, a 15th- and 18th-century building the Sterns restored as part of the offices when the company moved here in 1996.

The Sterns, who have been married 15 years and have two teenage children, say they don’t share an office, noting that their tasks are markedly different. (“I work, she draws,” jokes Mr. Stern.) But they do come together to brainstorm ideas. “We have specific meetings with creation and for the development of the movement,” Mr. Stern said. “Both come together. That’s how we work, and it’s important.”

With 21 basic calibers and some 100 patents, Patek Philippe is synonymous with technical innovation and thin movements, all of which are made inhouse alongside some 10,000 components.

Understanding the company from the inside out has been a kind of baptism for the Sterns. “After so many years you get this feeling inside you,” Mr. Stern said. “The DNA comes in.” That inherent understanding of the house is especially important to Ms. Stern. Like any creative director of a storied watch house, she balances a company archive (a museum houses nearly 2,000 watches and antiques ranging from the 16th century to today) with new design technologies.

“It’s not so difficult to find the right piece,” Ms. Stern said. “It’s finding what’s natural and in our DNA It’s important that the client will wear the watch and not just put it in the safe.”

Customer preference is where Mr. Stern comes in. He spends as much as four months a year on the road (“My grandfather, and father also, always said you have to travel”), gathering client opinion. “You understand what they like and don’t. But it’s not easy,” Mr. Stern said. “They expect Patek Philippe to surprise them — and that also is our goal.”

According to the company, its sales markets are split: about 45 percent in Europe; 30 percent, Asia; and 15 percent, the United States. But the Sterns note that they do not create watches for different regions. “It’s one watch for the world,” Ms. Stern said. “This is a challenge.”

On her wrist is a Ref. 7130G World Time, its usually brown strap swapped for a red alligator one. Introduced in 2011, the watch almost never reached the market.

“When she proposed a dial like this, I looked at her and said ‘no’,” Mr. Stern recalled. “I didn’t like it that much and thought it was maybe too aggressive for Patek Philippe. But that is also why I asked Sandrine to work on the ladies’ line: because I’m a man. I can go up to 80 percent but will never wear the watch. It’s a ladies’ watch. I needed a feminine point of view.” Eventually he gave his blessing but not without a loving warning: “I told her it won’t be a success but that you’ll learn from that.”

The watch, priced from 33,560 pounds, did well, of course (“That’s why you need both men and women to work together!” Mr. Stern said, laughing) — as has its ladies’ business generally.

According to John Guy, a luxury analyst at MainFirst Bank in London, women’s watches are estimated to make up 50 percent of Patek Philippe’s sales (the watchmaker does not comment on performance), positioning it well in a market that is forecast to grow 1.5 times faster than the men’s sector.

The company has been introducing more complicated ladies’ watches, partly in response to demand by women purchasing watches for themselves but also to the often-infectious nature of haute horology itself. “Sometimes their husbands are wearing a Patek Philippe and they give that passion,” Ms. Stern said.

For Mr. Stern, his preferred watch is a Calatrava Ref. 5527, among the house’s most recognized designs. But during the interview he wore a Minute Repeater Ref. 5208, a watch with more than 700 components and the house’s second most-complicated watch now in production. Mr. Stern said he was “testing” the watch. (“It’s not time for me to own such a watch. I don’t feel I deserve it.”)

The timepiece, which sells for around $1 million, is “very complicated so people will think, ‘Wow, it’s too fragile’,” he said.

Not that the price tag fazes him. “I don’t see the price, I see a watch,” he said, before intentionally banging it against the table. “That’s what you have to do,” he said, shrugging. “That’s what my clients expect of me.”

The company manufactures only around 58,000 watches annually, with its 2015 revenues estimated at 1.1 billion Swiss francs, or $1.12 billion, Mr. Guy wrote in an email. Considering its average retail watch price is 21,000 francs, he puts the company’s operating profit margin at 23.8 percent, at the industry’s higher end. And Patek Philippe watches are known for keeping their value, continually breaking auction records. For example, at the Phillips sale in Hong Kong in December, a 1985 white gold, perpetual calendar model sold for $1.6 million, the highest price ever paid for a wristwatch at auction in Asia.

Looking ahead, Mr. Stern says a top challenge will be managing the company’s retail network. It has 440 sales points in 67 countries, and only recently expanded beyond its three fully owned salons in Geneva, Paris and London to include about 20 Patek Philippe boutiques operated in partnership with retailers. The selection process is stringent and becoming a retailer can take two to five years. “We get to know each other, to understand their problems and they get to understand ours,” he said.

In 2010, he even reduced the number of dealers worldwide to 425 from 750 as he felt the house could not produce enough stock to satisfy demand while retaining quality. With dealer numbers now at a more manageable level, he said, they can be better educated and trained. “This is the challenge for today and tomorrow: to give retailers, sales staff and after-sales service all the knowledge they need to explain who we are and what we are doing. Believe me, it takes a long time.”

But it seems that once in, you’re part of the family. Beyer Chronometrie, on Bahnhofstrasse in Zurich — the Fifth Avenue of that Swiss city — stocks some 400 Patek Philippe pieces ranging from 10,000 francs to more than 1 million. It has been in partnership with the watchmaker since 1842, something that makes its owner, René Beyer, very proud. “Patek Philippe really tries to keep things as a family,” he said. “They are very traditional in this regard.”

G. Collins & Sons in Royal Tunbridge Wells, England, shares a similar sentiment. A Patek Philippe retailer for slightly less than 10 years, it stocks some 60 pieces. And Harry Collins, who also is Queen Elizabeth’s personal jeweler, calls his retail partnership with Patek Philippe the “ultimate agency.”

Unlike large watch conglomerates that solely focus on sales, Patek Philippe “truly cares,” he said. “They are so professional — we share the same values of quality, service and care for our name.”