A bit of television news took me by surprise the other day: The series “Strike Back” was renewed for a sixth season — and not only have I never seen an episode, I’d never heard of it.

These days, it’s pretty easy never to have seen a TV show, even one that has been on for years. ABC’s “The Middle,” for instance, will end a nine-season run next month … without my having seen any of the eventual 215 episodes.

But I’d heard of “The Middle,” as well as “House Of Cards,” “The Last Ship,” “Survivor,” and “Chicago P.D./Fire/Med/Justice/Sanitation” among others that might or might not still be running.

“Strike Back,” though, that one had me stumped. It airs via Cinemax (which is likely the biggest reason it had escaped my radar) and while its renewal was for a sixth season, it began in 2010 (even I can do that math) and has produced only 43 episodes.

Forty-three episodes over six seasons? Heck, “Gunsmoke” produced 39 alone in its first season … on its way to 635 hours of Marshal Dillon and Miss Kitty spending 20 years not having sex. (Of course, we’re discussing primetime series here; venerable “General Hospital” passed the 14,000-episode mark in February — and those folks more than make up for Matt and Kitty’s abstinence.)

“Gunsmoke” ruled during the era when — if you had the proper antenna and were lucky — you could view all three networks (from a safe 6 feet away), plus maybe a PBS station and one or two fuzzy local stations through that mysterious U-setting on the dial.

That is, when TVs still had dials that we were advised not to touch until the set sizzled and crackled off at night and the screen drained dark, down to a little white dot.

It’s unlikely shows such as “Strike Back” will ever again reach 635 episodes. Even broadcast network series start descending the back side of the hill after they reach the magic number of 100 episodes oft-cited as needed for syndication purposes.

The pay-cable and streaming services that launch series now, meanwhile, entice movie actors into lead roles with big paychecks for “seasons” limited to between six and 13 episodes.

“Big Little Lies,” for instance, was a huge critical and ratings success for HBO last season — with Oscar winners Reese Witherspoon and Nicole Kidman in lead roles — and produced just seven episodes. It’s now filming Season 2, and actually has amped up the star power by casting Meryl Streep in a supporting role.

Along with reduced production, though, it’s the sheer volume of series that will keep shows from setting any endurance records.

Take a guess as to how many original scripted series came through the various TV platforms in 2017.

Wrong.

The actual answer, according to a study by the FX Network, is ... 487. Now, think about how many shows you watch on even a semi-regular basis … and you can see why a “Strike Back” can fall through the cracks. That heapin’ helpin’ of TV hospitality means that if viewers don’t come back quickly in today’s landscape, you’ll be canceled faster than ABC’s “Turn-On” — the infamous 1969 variety series about which, legend has it, the decision to cancel it was made before the first episode finished airing.

One of the guests on “Turn-On,” coincidentally, was Tim Conway — who used to have a license plate reading “13 WKS” — referencing the once-traditional length of time a show would air before being canceled … the shelf-life of many of the comic actor’s projects. Today, that would be seen as the norm.

All of which makes those shows that seem to be running on dissipating momentum at this point a dying breed.

For instance:

“Repeat after me. I would like …”

“I would like …”

“… to feed your fingertips …”

“… to feed your fingertips …”

“… to the wolverines.”

“… to the wolverines.”

And, with that, “Saturday Night Live” began a 43-year run that will reach 847 episodes this week. (Well, to be historically correct, it began as “Saturday Night” and only added the “Live” after the cancellation of “Saturday Night Live with Howard Cosell” — yes, that Howard Cosell — which ran for 18 episodes.) “SNL” has been on the air for so long that children who were born midway through its run are now old enough to consider the show too square to watch.

“Saturday Night Live” (without Howard Cosell), being a sketch-variety show, gives it the sort of flexibility that can’t be enjoyed by scripted series that depend on maintaining their casts and storylines. The next longest-running show by episodes — “The Simpsons” at 633 — doesn’t have to age its characters or care about maintaining a narrative “bible” … although the voice actors who’ve been there from the start deserve some sort of medal.

Which brings us to a primetime offering such as “NCIS,” which marks its 350th episode coming Tuesday.

The supporting cast has changed on what’s known as “the mothership” (having given birth to spinoffs set in Los Angeles and New Orleans) and now, 15 years in, original cast members are either leaving (Pauley Perrette) or having their screen appearances reduced (David McCallum).

That will leave leading man Mark Harmon — whose 350 “NCIS” episodes leave him 78 shy of the 428 hours Mariska Hargitay has logged starring in “Law & Order: Special Victims Unit.”

It’s doubtful either has had time to watch an episode of “Strike Back” … so I’m in good company.

Mail Tribune senior designer Robert Galvin, who can be reached at rgalvin@rosebudmedia.com, has seen the new series “Deception,” which feels a lot like “Castle,” mixed with a little bit of “Remington Steele.”