nouns - Why it is "Okun's Law" and "Philips Curve" rather than "Okun Law" and "Philips' Curve"?

How exactly do these kinds of compound words work?

"Okun's Law" and "Philips Curve" rather than "Okun Law" and "Philips' Curve"?

Is there any grammar book I can look for?

Answer

There is no rule, different writers choose different styles. Without moving from my desk I can find the following examples of references to the same thing:

1. Bayes Rule


2. Bayes' Rule


3. Bayes's Rule

and then the same all over again but calling it a theorem rather than a rule.

If the proper name is not in a possessive form, then sometimes the definite article is used, as in "The Bayes Rule" but even that is not standardised.