Everyone said the right things, refusing to get out ahead of themselves and allowing Matthew Schaefer space to prove he should start the season on the Islanders rather than anointing the 18-year-old.

Even so, there was no drama or question over Schaefer’s inclusion on the 23-man Islanders roster, which was submitted to the league Monday.

Schaefer was selected by the Islanders 101 days ago and the last time there was any doubt about where he would be when the season opened was, at a minimum, 100 days ago.

“He had a great camp,” general manager Mathieu Darche said. “You saw it all. His skating abilities, but just the way, overall, he’s conducted himself in practice. The way he works in practice, the way he played in those games. He got better as camp went on.

“Even his first game on the road in Philly against basically their whole [NHL] lineup, he made a mistake in the first. It didn’t rattle him. [He] had a good game after that. So he’s proven that he deserves to be in the lineup on Thursday in Pittsburgh.”

The slide provision in NHL entry-level contracts allows for players to be sent back to junior without losing a year of their deals if they play nine games or fewer, so the 10-game milestone will be important for Schaefer to reach, as it formalizes that he will spend the whole season on Long Island. Like making the roster, though, something would need to go dramatically wrong for that to be anything more than a fait accompli.

Defensemen, the conventional wisdom goes, need about 200 NHL games to develop. In an era when it is normal for the No. 1, and often the No. 2, overall picks to jump straight to the NHL as 18-year-olds, it’s no coincidence that the last top selection who did not do so was defenseman Owen Power in 2021.

Just four No. 1 overall defenseman have played more than 10 games as 18-year-old rookies: Gord Kluzak (1982), Roman Hamrlik (1992), Aaron Ekblad (2014) and Rasmus Dahlin (2018). Schaefer, almost certainly, will be the fifth.

“You’ve seen teams having young guys, they keep them up [in the NHL] and manage their workload. But like I said from the start, the way he’s gonna play is gonna dictate what we do,” Darche said. “He’s completely earned his spot on the team and in the lineup on October 9. He will be in the lineup. And we’ll take it as we go.”

Schaefer will start the season on the third pair with Scott Mayfield, a partner whose defensive acumen should give him some cover to jump into the rush. Over four preseason games, Schaefer’s skating ability was a consistent plus, though he did seem prone to occasional errors in the defensive zone.

“I lived it when I was playing, I was 20 years old after I started playing in the NHL,” coach Patrick Roy said last Thursday after the Islanders’ preseason finale in Philadelphia. “There was nights where you can lose your confidence very easily. So I don’t want it to happen to him. I want him to stay the course, focus on what he needs to do. There’s nights where — just keep it simple.”

The Islanders are betting that Schaefer has the maturity necessary to handle it when mistakes inevitably come, as well as dealing with the spotlight that comes with being the No. 1 pick in New York.

The tests will come right away, with Schaefer set to line up opposite Sidney Crosby and Alex Ovechkin in his first two NHL games.

“His skating ability, his maturity, being an 18-year-old playing professional hockey, being in the NHL in a market like New York, I think his maturity really gave me confidence that that won’t be an issue,” Darche said. “From the first day we sat with him at the combine, that’s what stood out. So that’s what comforts me that he’s ready for this. And we’ll start the season and see where it goes at this point. He’s earned his spot in the lineup for that first game.”