The stories about Apple keeping things secret usually go about protecting their business secrets from normal people, up to doing probably illegal actions.

Using deniable, one-time keys etc. are... not that unusual. In fact I'd say I'm more worried about the use of random USB keys there instead of proper KMS system.

(There are similar stories with how doing a cold start can be difficult when you end up with a loop in your access controls, from Google, where a fortunately simulated cold-start showed that they couldn't access necessary KMS physically to bootstrap the system... because access controls depended, after many layers, on the system to be cold-started).

they used smartcards, not usb keys

Which probably were just key transport devices from offline secured KMSes

What's funny is that, in all these orgs, it ends up being the low-tech vulns that compromise you in the end. Physical access, social engineering, etc. However, I'm really impressed by the technical lengths Apples goes to though. The key-burning thing reminds me of ICANN' Root KSK Ceremonies.

Destroyed? Where? In all places where they were stored? Or just in some of them? How can you tell? You still need to trust them they didn't copy them somewhere.

It's impossible to use any technology if you don't trust anyone.

Any piece of technology MAY have a backdoor or secondary function you don't know of and can't find out without breaking said device.

That was the point of my response. Somewhere in the chain one must trust something without any proof.