The Sochi Olympics have only just ended but NBC Universal is already gearing up to sell ads in its coverage of the 2016 Summer Olympics in Rio.

NBC Universal has plenty of recent success to boast about as it approaches advertisers: Online streaming for the Olympics hit new records, viewership in peripheral parts of the day has been strong and the games put the fledgling NBCSN on the map. There's also been a halo effect on the rest of NBC's schedule, providing a massive lead-in to Jimmy Fallon's debut as the new host of "The Tonight Show;" and boosting the "Today" show ahead of ABC's "Good Morning America" for the first time in two years.

But when it comes to prime-time, where about 80% of ad dollars are allocated, there's less to discuss, as Sochi fell short of some of the ratings guarantees it promised advertisers and the audience is aging up.

And that could change the conversation with advertisers around the Rio games.

For one, NBC will be looking more closely at cable, said Seth Winter, exec VP-sales and sales marketing, NBC Sports Group and NBC Universal News Group.

In the 6 a.m. to 3 p.m. time slot, NBCSN averaged 1.6 million viewers during the first 13 days of the games, up from 714,000 viewers during the same period in the 2012 London Olympic. The network aired all of the figure skating competition live on NBCSN.

NBCSN has also been bolstered by its coverage of hockey, with the face-off between Team USA and Russia watched by 4.1 million people despite its 7:30 a.m. ET airing.

Mr. Winter said he also expected more money to find its way to digital platforms.

The games garnered about 22 million video viewers, up about 5% from the London games, with about 53 million people visiting across all of NBC Universal's digital platforms. The Sochi games marked the first time NBC Universal has made nearly every event available streaming live.

Friday's hockey semifinal between the U.S. and Canada was live-streamed by more than 2.1 million unique viewers. NBC said it believes this is the largest TV Everywhere-authenticated streaming audience to date. The figure is on par with NBC's stream of the 2012 Super Bowl, which did not require a cable or satellite subscription and attracted 2.1 million unique viewers, according to the network.

NBC's weekend viewership, which averaged about 11.6 million viewers, was up about 5% over Vancouver and 24% compared with Torino. In late-night, NBC averaged about 5.7 million viewers, a 19% boost over Vancouver and 15% increase from Torino.

"Prime-time is still the engine that drives Olympics investment and always will … But other peripheral dayparts are playing a bigger role," Mr. Winter said.

As of Saturday, NBC's taped prime-time coverage of the games averaged 22.5 million viewers and a 12.9 household rating. (A ratings point represents one percent of total U.S. TV households.)

While that topped the approximately 20 million viewers Torino averaged, it's down from the more than 24 million viewers Vancouver averaged.

The Olympics also continue to age up, even with the addition of new extreme sports events such as snowboard slopestyle that typically attract a younger audience. In the all-important 18-to-49 demo, Sochi averaged a 6 rating during the first week of the games. That's down from both Vancouver and Torino, which averaged an 7.1 and 6.2 rating, respectively, during the same period.

Even AMC's "The Walking Dead" pulled a larger audience in that demographic when it was up against the Olympics on their first two Sunday nights.

But media buyers said they aren't overly concerned with the prime-time numbers, noting that the highest ratings still come in that time slot.

The dip from Vancouver is also not all that surprising given those games were predominantly aired live in prime-time while Sochi necessitated a significant delay.

"We are not using Vancouver as the benchmark," one buyer said.

Overall, the advertising community has been happy with NBC Universal's coverage.

"NBC is doing well considering the events are not live in prime-time," said Gerri Donini, senior VP-national broadcast, RJ Palmer. "NBC's expectations were a bit higher, but not by much"

Still, NBC had to dole out some make-goods to advertisers, according to media buyers. NBC promised some marketers as high as a 15.5 rating, according to buyers. Though other advertisers were said to receive household guarantees around a 13 rating.

Mr. Winter said NBC had planned accordingly, reserving some inventory before the games for make-goods. Mr. Winter noted that they did not see major shortfalls in prime-time.

While Mr. Winter and his team will spend the next few weeks analyzing coverage, he said early results show a greater brand recall for ads running during the games.

According to NBC, based on 28 ads they found that the same spots running inside the Olympics had a 57% brand recall and 82% higher message recall than those that ran outside of the games.

Looking to Rio, which is only two hours ahead of the east coast, media buyers expect the focus to return to TV since more of the games will air live in prime-time.

Ultimately, it comes down to viewers' desire to watch sports live and whatever platform delivers the content at that time, according to a buyer.