My point is that although many only think about ISO C libc when talking about C's standard library, the reality is that with a few exceptions, libc always goes alongside POSIX across the large majority of platforms with a C compiler.

So in reality POSIX complements libc as C's "runtime platform", even though ISO C never considered to make libc that big.

My historical context is how I experienced how things went, throughout the media we had available at the time.

I surely welcome factual corrections when I fail off the mark.

Everyone benefits from learning proper history facts.