I suspect that signatures in cases, Easter Eggs, model names, System names, MLB architectures and the like (which often show a high degree of literary awareness, impish mischief and invention in Apple's staff), were part of a (then) culture of swinging devilment and irreverence. Take the BHA and LAW architectures (alias Carl Sagan).
Art is where you find it, and not always where it is paid for. Take the oohs and aahs about Primitive (Western) Art. Picasso must have taken not more than a minute for his long-lived impression of a compact Mac. Only someone in a determined search for art could find it in Bakelite teaspoons, or urea-formaldehyde backscratchers. I cannot deny (and am not yet mad enough to try) that there were finely-crafted articles, &c. in older plastics, but that they were intended, in materials of then-unknown longevity, to last for a thousand years and one year, I have to doubt. Their functions were to last until the next model replaced them. And that is still the case with most crafted (including carry-bags) plastic.
A PTFE bushing for the stirrer of a liquid nitrogen bath (to get imaginative, hypothetical and exemplary for a moment) may have more swinging on its reliability, but it will be replaced, just to ensure reliability, long before it wears out. Most other plastic used is aimed at a decade or less. You have the advantage of me in referring to Apple Design, but I am also aware that Apple's Platinum was our yellowing Beige with enough blue masking pigment to prolong the time until arrival of galloping yellow, which is still a much shorter interval than forever.
de