Great example, and I'm old enough to have also wondered why those "nc" pins on valves and ICs clearly did do something.

As you frame it, it's "What the eye doesn't see the heart doesn't grieve". Definitely apropos the making of burgers and sausages.

Now we have a different discussion, about "internal" or "external" legibility.

We used to live in a world of high trust in vendors. Those days are gone. Vendor malware is a massive and growing problem and supply-chain legibility is a hot topic.

FWIW I'm arguing the fully open position. Unless you've desperate trade secrets, there is no "internal". And if you've a 16 bit register that's 65536 entries, most of them sparsely documented as "no op". And if a researcher finds it does something,... it's suspicious by default.

This "no user serviceable parts" is an old schism in technology. Today we have almost blanket rights to repair and openness is the new security model.