They're solidly pre-digital. Somewhere, the individual frames were drawn/painted on cel, were they not? In principle, remastering should still be possible.
In fact there's an episode of the Simpson's where Bart buys an Itchy & Scratchy animation cel and is disappointed when it's just a segment of Itchy's arm (or something like that).
Guilty as charged! This brings back a memory from around 1980.
I ordered an animation cel from Original Animation Art (Starshine Group).
You had to mail them a check and a description of what you were looking for, and hope for the best.
The first one they sent me was a little bit better than Scratchy's arm, but not by much. I returned it and asked for something with the entire character in it.
They sent Daffy Duck nearly off the edge of the frame with a nasty scowl. Not fun to look at.
For the third try, I asked if I could please have something with the character smiling and in the center of the frame. And they sent a wonderful cel of Porky Pig from A Connecticut Rabbit in King Arthur's Court!
It looks very much like this one, but only Porky and not the background:
I shouldn't have said never had a film negative. They likely scanned hand-drawn cells to film, then transferred that to tape. At the time they likely saw the NTSC tape as the master.
It would take a ton of work, especially for a show as long-running as The Simpsons. The original materials probably aren't even available anymore.
I believe the reason they were able to remaster lots of old Japanese anime OVAs in HD is because the animation was recorded to film first. I wouldn't be surprised if the Simpsons just used videotape instead.
