An additional thought regarding Up-scaling: Until about 7 years ago, almost all digital VFX (including on True Lies and Titanic mentioned in the article: done by Digital Domain at the time) for film was still being rendered/delivered at 2K (other than occasional larger format things like IMax), so it's almost certain that in the 90s/2000s, while the plate footage on film might in theory have been very high resolution if scanned (if the film stock was good enough), the VFX delivered for it will have been only good enough for 2K resolution as that's what it was rendered/delivered at originally.

So anything "requiring" a 4K release would almost certainly have had to have been up-scaled, unless the studio managed to get the original VFX vendor to re-render/comp and deliver 4K footage which I've heard of happening in a few cases (Star Wars re-releases, some Pixar stuff), but other than that isn't generally done and the VFX can only be upscaled from the "original" delivery.