In the whole history of American television, only one primetime scripted series has crested 600 episodes: the venerable Western Gunsmoke, which produced 635 episodes between 1955 and 1975. (TV shows produced far more episodes back then than the 22 episodes per season typical of broadcast series today.)

But on Sunday, October 16, another series will join Gunsmoke in the 600 episodes circle. That series is The Simpsons, which has run 28 seasons since it debuted in December of 1989. It should pass Gunsmoke in the spring of 2018 (it’s already producing episodes for the 2017-18 season) — and who knows? It might even make the push for 700 episodes after that.

But how many of those episodes were good? That’s the question plenty of people ask — and the fact that the answer is probably somewhere around "one-third" is the reason many wish the show had stopped somewhere in the late ’90s. (I would say the show’s first eight seasons are its best, but could see making an argument for seasons nine through 11 as well.)

But here’s the thing: The Simpsons could produce genuinely terrible seasons of television for the next 50 years, and it wouldn’t take away from the achievement of those first few seasons.

And when you consider that the show is still, all things considered, pretty darn good, that makes it even more impressive. The Simpsons hasn’t just made it to 600 episodes. It’s made 600 episodes of TV, where the vast majority were at least mildly entertaining and many were all-time, stone-cold classics.

When should bad seasons of a TV show be held against the good ones?

I have a rule about whether to hold bad seasons of a TV show against the good ones: Do those bad seasons point out flaws that were present in the early seasons, which were plastered over with great acting or writing or directing? Do the bad seasons, in effect, open up little holes in the show’s base that become more troubling the longer you look at them?

For a good example of a show where I think a bad season damaged my opinion of the series overall, look at 24. That show’s sixth season was a catastrophe, but in a way that underscored how the series had always been flying by the seat of its pants when it came to its storytelling. That it had made it so far was commendable, but it still revealed just how little it had been in control all along.

For an example of a TV show where an infinite number of bad seasons couldn’t hurt the good ones, well, just look at The Simpsons. Bad episodes of The Simpsons don’t point out flaws in the underlying template — they just fall kinda flat.

Related The Simpsons is still really good

All TV shows are going to lose something the longer they run and the more their audience starts to catch onto their rhythms and what they do. There’s no way, 28 seasons in, that The Simpsons could surprise anybody.

And there are other ways you can judge just how the show has shifted over its nearly three decades on the air. When it began, it was Bart’s show. The 10-year-old was at the center of most stories, and he was the series’ breakout character. He got many of the best jokes, and most of the show’s relationships ran through him.

But in the show’s best period — which I would say was roughly from seasons four through six — it slowly shifted from a series about Bart to a series about his father, Homer. As the show’s writers got a little older and had kids of their own, they started to identify more with the doltish Simpson patriarch, for better or worse.

This, of course, oversimplifies things a bit. When The Simpsons was firing on all cylinders, it could tell great stories about any of the four main characters — Bart, Homer, Lisa, and Marge. But the fact that the show shifted from having Bart as its main character to having Homer as its main character was probably why it was able to last so long and avoid becoming a flash in the pan. Homer might have been a big jerk, but he was also a more durable protagonist for the show.

Holding The Simpsons’ post-1990s seasons against it is pointless

But now, over 20 years after that point, the writers don’t have an obvious point-of-view character anymore. It’s probably Homer, but everybody involved seems to realize just how difficult it is to find new stories to tell about any of the four main characters. They’ve spread their net wider and wider, looking for characters to tell stories about, with seemingly every citizen of Springfield, no matter how minor, getting a chance in the spotlight.

That means that the show is, inevitably, less outstanding than it once was. The combination of lack of stories for the main characters and the ever-widening net means that the series can sometimes feel centerless.

But individual episodes almost always have a handful of gags that work, and the show is still (mostly) committed to the solid storytelling that set it apart from its many clones. At least once or twice per season, it turns out an episode that can stand with the best from early in its run.

But, again, even if The Simpsons wasn’t capable of that, why would it take away from what the series could do at the height of its powers? For my money, that eight-season run is the single longest run of great TV in the medium’s history. There are a handful of bad episodes in there, but for season after season, it was unquestionable that the show was among TV’s best.

What’s more, the later, less essential seasons haven’t somehow revealed flaws within the program’s classic years. Instead of pointing out issues that should have been apparent all along, they’ve simply expanded the series to the point where it feels like it could tell a story about essentially anything and have it be a Simpsons episode.

Indeed, if there’s one thing that The Simpsons and Gunsmoke have in common — and it might really only be the one thing — it’s that both of them take place in worlds that feel bottomless. The Western’s central town of Dodge City ended up being at the center of hundreds of sharp morality plays, while the comedy’s Springfield became America in a microcosm, a place that boasted anything and everything the writers needed to mock the country they lived in.

The Simpsons is probably closer to its end than ever before. I have grave doubts it will make it to 700 episodes. But its achievement shouldn’t be sniffed at, simply because it couldn’t continue to make TV at the level of its first eight seasons for 30-some years. No, The Simpsons is a tribute to TV’s elasticity, to the idea that all you need for a great TV show is some good characters, a great world, and a premise that could stretch in any direction.

Watch: These 11 actors play more than 100 Simpsons characters