Compliance here means compliance with the CA/B Forum Baseline Requirements (and similar other policies), which cover a lot of operational obligations, from character encoding to physical security.

That's true for some handles in Win32, but (since we're talking about classic MacOS) Win16 handles were usually NEAR pointers inside kernel segments.

True! That was a disaster; only 64K (16 bits) handles were possible across all processes. Many APIs had to be deprecated and redesigned when it went 32-bit.

I've argued for using uuids for handles from here on out. They are endless; no effort to coordinate handle spaces is ever needed; they work locally and on the network; on some architectures they are even a register width scalar.