When they started their groundbreaking “A’s Access” plan — which is essentially a full 81-game subscription to the Coliseum — the A’s knew there would be some hiccups and they would have to make some tweaks for next year.

What they didn’t know was that in the first year of sales, season-ticket totals would skyrocket. The A’s sold 9,535 Access plans — doubling the previous year’s season-ticket totals.

“I would never have estimated double,” COO Chris Giles said on the “A’s Plus” podcast. “I don’t know if we had an estimate. We were building something that had never been done before. We were taking core membership principles from industries well outside of sports, things like gyms and country clubs and software as service models.”

Baseball took notice, especially when the A’s data showed that Access plan members are, on average, 11 years younger than previous season-ticket holders. One of the top concerns around the sport is the graying of the fan base — could a subscription base help attract the next generation? Commissioner Rob Manfred met with owner John Fisher, CEO Dave Kaval and Giles to hear more and asked for a summary. Twenty of Giles’ baseball counterparts have discussed the business model.

Teresita Nuño, 37, of Calistoga, bought the A’s Access half-season weekend plan this year. She hadn’t had season tickets before, though she has attended games regularly for nearly 20 years.

“I was spending so much money going to games already, I thought, ‘Well, this will pay for itself,’ and it’s so much more rewarding than I’d even thought it would be,” Nuño said. “It’s well worth it.”

Attendance this season is up 64,021 from the same point last year, with home games against the Giants (typically sellouts) still remaining along with a hoped-for playoff stretch run. Oakland has only 79 games at the Coliseum this year after opening the season with two “home” games in Tokyo.

On Monday afternoon, the team announced changes to next year’s A’s Access plan, the result of customer feedback. Top on the list: Fans wanted to be able to use the plan as they’ve typically used season tickets — sharing a set of seats with other families or giving them to friends for a week. The inability to transfer memberships frustrated those who wanted to go in on tickets with their longtime groups.

“A lot of people were like, ‘Hey, why can’t I just give my pass to someone else?’” Giles said. “No one would ever think, ‘Hey, I’ll just give you my gym membership and you go use it today and I’ll go use it tomorrow.’ …. But we’ve had 100 years of one model and we’re getting people to think about it differently.”

For 2020, all fans with Access plans with seats for 24 games can add a full member for $199. Those with half-season or full-season plans can add members for $99.

“As we work through Year 1,” Giles said, “a lot of things we focused on for the 2020 version was really to address those two things: How can we make this program as simple as possible — but how can we make it as flexible as possible, to make sure whatever your use is, A’s Access works for you.”

Another expressed concern is that when fans with 10- and 24-game seats used the “access” part of the plan, attending games that weren’t in their seating plan, the areas to which they were restricted didn’t have a wide enough variety of food and other amenities.

“It was really difficult for us to deliver the level of service we wanted in that kind of finite space,” Giles said.

So in 2020, the plan is all access — every fan with a membership can go anywhere in the stadium.

In addition, the A’s are eliminating variable pricing for Access members. Should fans with a plan want to exchange their seats for a different game, they may do so without paying any additional charge for a more desirable night or opponent, no fees involved.

And every member, regardless of seating plan, will get half off concessions, 25 percent off merchandise and $10 parking.

“What we’re trying to do is get people to see the macro benefits of this program and see once you’re a member, we’re going to do everything in our power to make sure you have the most value-rich experience in baseball,” Giles said.

Anyone who would like to give the program a test drive may do so at Sunday’s A’s Access Day at the Coliseum, at which everyone in attendance will receive the plan’s discounts, including $10 parking.

The following day, A’s Access 2020 will go on sale, with plans starting at $396 per year. Next year, the team will provide digital credentials, too, to make it easier for fans to stop by the ballpark anytime without having to go home to find their lanyards.

Among the other findings this year: 50% of members have used their general-admission access to attend games other than those in their seating plan, and 4.6% of fans at the Coliseum are using the general-admission benefit.

“We’re finding it’s very much like a gym,” Giles said. “If you ask people how often they’re going to use their gym at the time of the purchase, they’ll say something like 10 times a month — actual utilization is much closer to four.”

Nuño said that she has found owning season tickets has brought her closer to family members; she found a cousin on social media and discovered those family members were A’s fans, too.

“I love the fact that I can stack tickets and bring larger groups to the park,” she said. “It’s been a great thing for bonding with family I didn’t even know I had — and they’ve been to more games than they’d ever been to because I have this plan.

“It’s amazing. I was spoiled before as an A’s fan. It’s phenomenal coming to games, but this year is the icing on the cake. I don’t know if I’d ever go back to not having season tickets after this because of the Access plan.”

Susan Slusser is a San Francisco Chronicle staff writer. Email: sslusser@sfchronicle.com Twitter: @susanslusser