I think TV shows tend to be much more of a mixed bag. The Sopranos (1999), The Wire (2002), and Firefly (2002) were all shows at the forefront of the current renaissance in dramatic television— they were all shot on film, but it's interesting that Firefly for example was natively 16:9 and cropped to 4:3 for its original run, whereas The Wire's "conversion" to widescreen has been a matter of some more controversy, eg: https://www.techhive.com/article/2854439/hbo-remastered-the-...
Another interesting aspect of Firefly is that the pure VFX scenes (eg spaceship exteriors) were rendered originally at 480p, so when you watch the Blu-ray version of the show, you can see a bit of an awkward transition where the shots of the actors are gloriously crisp, but the space scenes are clearly upscaled.
Friends was also shot on film, and cropped to 4:3 for broadcast. Like Firefly, Friends also had unintentional things (crew, microphones, un-dressed sets, etc) appear in the edges in 16:9. While most were probably edited out before the uncropped 1080 re-release; some unintended things remain, which I personally really like seeing.
Additionally, like Firefly's pure VFX, some footage in Friends also appears in SD in the HD release (seemingly either because the original film stock was lost, or it wasn't originally shot on film), with the zoomed 4:3 SD vs 16:9 HD sometimes changing mid-scene, and …that too I find a humbling reminder of the quality of yesteryear.
I've been noticing some of the same with The X-Files. There are seemingly random shots with lower quality, and any shot with heavy VFX looks original, but most of it now looks quite sharp.
I remember having a distinctive moment of clarity watching Seinfeld reruns in 16:9 HD. Did they have the foresight that it would be a classic making billions in syndication?
Seinfeld started airing in 1989 a decade before American HDTV so they probably didn't foresee the aspect ratio of televisions switching from 4:3 to 16:9. 35mm film likely gave them more high-end options than the cameras and lenses meant for broadcast. It would also give them more wiggle room if they needed to re-frame a shot in post.
Personally I find most of the 16:9 crops of old shows in syndication quite jarring, especially because in any shot where the formerly extra width doesn't work the editor is forced to vertically crop the original. Here are some screenshots comparing 4:3 and 16:9 Seinfeld and ...eek
So I would ask if maybe the image was cropped for the 16:9 conversion.
Update—here's what Wikipedia says: “Unlike the version used for the DVD, Sony Pictures cropped the top and bottom parts of the frame, while restoring previously cropped images on the sides, from the 35mm film source, to use the entire 16:9 frame.”
35mm stills cameras normally use a 3:2 frame. Television shot on film typically used movie cameras that shot at 1.85:1 and then cropped to 4:3.
But different shows handled the aspect ratios differently in their widescreen re-releases. Seinfeld included slightly more horizontally than the original TV release but still cropped a significant amount from the top and bottom. That 70s Show as one example that was also shot on 35mm film included the whole original 4:3 frame plus extra on the sides.
Could it matter that movie cameras use the same film but vertically? I'd be more inclined to stretch frames horizontally if I was designing a cinema camera, because that means the film run slower.
Another interesting aspect of Firefly is that the pure VFX scenes (eg spaceship exteriors) were rendered originally at 480p, so when you watch the Blu-ray version of the show, you can see a bit of an awkward transition where the shots of the actors are gloriously crisp, but the space scenes are clearly upscaled.