‘Hard Knocks’ is still enjoyable two decades in, which makes you wonder how a Patriots season would go

“Hard Knocks,’’ the entertaining if formularized HBO series that documents a single selected NFL team’s training camp each summer, still feels relatively fresh.

So I was somewhat caught off guard by the recent realization that this year’s five-episode arc, which features the Dallas Cowboys and owner Jerry Jones’s massive ego for the third time in the show’s run, marks two decades since it debuted in 2001 with a peek behind the curtain of the defending Super Bowl champion Baltimore Ravens.

The Patriots’ dynasty began that same season, of course, and it remains fans’ loss that the six-time Super Bowl champions are yet to appear on the program. The closest Patriots fans have come to seeing favorite or familiar Patriots on “Hard Knocks’’ is when they were on other teams’ rosters – an undrafted free agent received named Danny Amendola trying to make the Cowboys in 2008, or Vince Wilfork showing off his basketball skills and big personality with the 2015 Texans. Oh, and there was the less-than-mesmerizing quarterback battle with those Texans between Brian Hoyer and Ryan Mallett.

There are semantical reasons why the Patriots haven’t been on the show: A team can refuse to be selected for “Hard Knocks” if it has a first-year head coach, has appeared on the program in the past 10 years, or – and here’s the Patriots’ out — has reached the playoffs in either of the two previous seasons. The Patriots have not missed the playoffs in back-to-back years since Pete Carroll’s last season as coach (1999) and Bill Belichick’s first (2000).

Franchises can volunteer to be the featured team – one gets the sense Jones and the Cowboys are the always-ready-and-willing default guest, like Tony Randall during David Letterman’s late-night heyday. But there’s probably a better chance the Jets win the Super Bowl this year than there is of Belichick ever volunteering to let the cameras in, even with his long-standing relationship of mutual admiration with NFL Films.

If the Patriots miss the playoffs this year, they would be eligible to be chosen next season. With a reloaded roster, it’s hard to fathom that happening. But it is interesting to think about what it would look like, and how fascinating it would be to get a glimpse into Belichick’s preseason process.

Watching an obviously competent head coach is a rarity on “Hard Knocks.” In the 17 seasons an individual team has been featured – the show didn’t air from 2003-06, and a highlights edition from previous seasons aired in ’11 —  there have been far more coaches that came across as overmatched or underwhelming than those that made a viewer say, “I can see why he’s the boss.”

The ’02 Cowboys’ wetsuit-wearing Dave Campo, the ’12 Dolphins’ milquetoast Joe Philbin, and current Cowboys coach Mike McCarthy, who in this season’s first episode featured a groan-inducing motivational tactic drawn from “Austin Powers: The Spy Who Shagged Me,’’ all made this viewer skeptical of their team’s possibilities no matter what their talent level.

McCarthy at least makes for amusing television, with his collection of weary aphorisms and exhortations from a 1985 Mike Ditka Mad-Libs collection. “I want you [expletive] geared in,’’ he implored his team before their second preseason game, a loss to the Cardinals. “Let’s turn this [expletive] up. I’m talking everybody, Let’s bring it to these guys.” These vignettes don’t offer a lot of intel on how the Cowboys plan to be a better football team this year, but it does seem to offer a clue as to why the Packers, who McCarthy coached from 2006-18, have won just one Super Bowl with Aaron Rodgers at quarterback.

The formula on “Hard Knocks” really hasn’t changed at all since that first season with the Ravens. There’s always a quasi-candid look at the team’s quarterback (this season opens with Dak Prescott talking about the aftermath of his brutal ankle injury last season), a sequence or two of another star struggling humorously with an everyday chore (Ezekiel Elliott, running back and inept gift-wrapper), and always, a tale of an underdog trying to make the team (this year’s subject, pass rusher Azur Kamara, whose family fled the civil war-torn Ivory Coast when he was a child, is the most interesting story this season by far).

And Liev Schrieber (best known in this office as the actor who perfected former Globe editor Marty Baron’s cadence and mannerisms in “Spotlight”) narrates it all, as he has each year since that first season except for 2007, when actor and Chiefs fan Paul Rudd did the voiceover honors when his favorite team was featured.

“Hard Knocks” remains as predictable as a checkdown from a confused young quarterback, but there are just enough candid moments and light chuckles to keep it satisfying. None of the teams that have been featured, however, are as interesting as a certain one that never has.