> The fact that Git, Python 3, SSH and nginx worked fairly ok implied they probably did some testing too.

Or it's a simple side effect of them being portable software. Since the same code has to work on very different ISAs like 32-bit x86 and 32-bit ARM, any architecture-specific code has to be cleanly separated, with a portable fallback. As long as the compiler can still target the "486" architecture, they'll work.

It's a different story with anything which depends on lower-level platform details, like the kernel or glibc's pthread.

> The kernel does a great job in maintaining backwards compatibility, the rest of the stack not so much... reply

No disagreement. But so far I did not encounter any issues with other parts of Linux other than the kernel. So the rest of the stack seems to do quite well.