SilverWook said:
I doubt Kenner was concerned about them holding up to the scrutiny of being put in the family slide projector at the time. Perhaps they rephotographed what they had handy in their archive?
That would be my guess. Here's a couple of scans of the "freeze frame" slides, you can see that they're not very sharp and the colors are kind of wacky. I also up put a scan of a similar scene I made from an actual film trailer for the se jedi so you can compare it with the slide. Theoretically, had this been an actual slide, it should have looked much sharper and more detailed than the film print (at least that's how it works in still photography, slide film is tops). That clearly isn't the case here though.
Stormies (freeze frame scan)
Leia (freeze frame scan)
Similar scene with Leia (actual film scan from SE trailer)
I scan at 4800 dpi so these images are massively shrunk down, if for any reason you want to see the full res images let me know and I'll post them.