[the_why_of_y]

> ANSI Common LISP lives up to that standard.

There is only one version of the ANSI Common Lisp standard, so it is trivially compatible with itself.

> C's versioning lives up to that standard.

Then how do you explain this astonishing work of art?

https://kristerw.blogspot.com/2016/07/code-behaving-differen...

[Annatar]

Easy: you tell the compiler which version of C you're compiling, and it churns right through it without a peep. Versioned formats, cornerstone of every good engineering implementation.