There’s a cast of unknowns, the ratings are spotty, and so they call in Prince and hand over a chunk of Saturday Night Live.

Reading the breathless press coverage of his upcoming, eight-minute jam (Rolling Stone: “What better way to celebrate the 30th anniversary of Purple Rain…), it’s easy to forget that the Purple One has played this rodeo before. In fact, Prince made his SNL debut 33 years ago, on Feb. 21, 1981. And if you think Cecily Strong and Co. have got troubles, you’ve never seen Charles Rocket play J.R. Ewing.

That infamous spoof of “Dallas” occurred during the 1981 night known as Season 6, Episode 11. It’s an SNL cast at the nadir of the attempted reinvention of the Not Ready for Prime Time Players, but it’s also something else, a rare hole in the Hulufied pop cultural canon. You can find 82 copies of “The Best of Chris Kattan” selling for as little as a penny on, but just try picking up Episode 11. It’s not for sale, it’s not streaming, it’s not available on some crinkly VHS tape on eBay.

Hence, we must ask: If a skit bombs on late night but is never repackaged for DVD, did it ever exist?

“Thank God in heaven,” Gilbert Gottfried tells me when I called to tell him I couldn’t find any video record of his Episode 11 performance as Reagan budget director David A. Stockman. “I say thank God for anybody who enjoys comedy.”

Back then, before his endless stand-up gigs and 11 years as the voice of the Aflac Duck, the ingeniously grating Gottfried was one of the unknowns hired to replace Bill Murray, Jane Curtin, Gilda Radner, Al Franken and Laraine Newman. The other new hires included Denny Dillon, Ann Risley and a former local TV anchor named Charles Rocket.

“It was like if in the middle of Beatlemania, you said, ‘okay, John, Paul, George and Ringo are leaving and we’ve got these four other schmucks you’ve never heard of and they’ll be the new Beatles,’” Gottfried says.

Executive producer Lorne Michaels was also gone, replaced by Jean Doumanian, the show’s associate producer. Years later, she would produce Woody Allen movies and a slew of plays and musicals. But in 1981, she was unfairly blamed as the woman who crushed Lorne’s creation.

“For me, it was agonizing,” says Joe Piscopo, who, along with Eddie Murphy, was the only cast member to survive Season 6. “I felt in every sense that we were ruining America’s favorite TV show.”

Doumanian, speaking Thursday by phone from New York, remembers getting a tape from Prince’s agent. He was just 22, hot off opening for Rick James but still more than a year away from releasing his breakthrough, “1999.”

“I was blown away,” said Doumanian. “He was just the most original act I had seen in a long time.”

Strangely enough, SNL booked Todd Rundgren as the musical guest. But the show, she said, had a spot for new talent. Prince would go on at the end, performing “Partyup” off 1980’s “Dirty Mind.”

It’s an electrifying performance and not hard to find. But it’s far from the most notable moment of Episode 11. That came during the closing farewells. Host Charlene Tilton, best known for playing Lucy Ewing on “Dallas,” is leading the standard wrap-and-wave.

Rocket is in a wheelchair, playing off the “Who Shot J.R.?” episode of “Dallas,” the highest rated on television at the time it aired in 1980.

Who shot J.R.? “I’d like to know who the [expletive] did it,” Rocket said on live TV.

“That,” says Piscopo, “was the beginning of the end of Charles Rocket right there.”

Not exactly. Rocket would be gone from SNL, but he would continue to act, playing characters in a series of films, including “Earth Girls Are Easy,” “Dumb and Dumber” and “Dances with Wolves.” He killed himself in 2005 at the age of 56.

So what to make of Episode 11? An NBC spokesman said it’s “unavailable due to shelf rights.”

“Oh, please,” says Doumanian. “I think they’re trying to forget it ever existed.”

Which is sad, considering that the episode features a double shot from then 19-year-old Eddie Murphy. He introduces “Mister Robinson’s Neighborhood,” his brilliant spoof of Mister Rogers, and does Stevie Wonder doing Tevye from “Fiddler on the Roof.”

“The truth is, if you think about Saturday Night Live, it wasn’t 72 minutes of non-stop laughter,” says Doumanian. “It was one great sketch or one great character and that’s what you would talk about the next day.”

I asked Doumanian if she had a copy of Episode 11. Turns out, she had kept videos of the season but, about 10 years ago, lost them in a fire.

As for whether Prince can save SNL – the show’s been up and down this season ratings-wise, but has clearly struggled to replace Seth Myers, Fred Armisen, Jason Sudeikis, Andy Samberg, and Kristen Wiig in recent years – she doesn’t expect anything Earth shattering. A little “Purple Rain” couldn’t hurt, though.

“I don’t think it’ll change the fortunes of the show but it’ll certainly bring the ratings up,” she says. “And people who tune it to see Prince, they may say, ‘I really like Saturday Night Live.’ I think I’ll watch next week, too.’”