I had to look both of those up, and you’re right. The rule is inconsistently applied for sure. This got me curious about where the so-called rule came from. Wikipedia says:

> Auto-eponyms may use either the possessive or non-possessive form, with the preference to use the non-possessive form for a disease named for a physician or health care professional who first described it and the possessive form in cases of a disease named for a patient (commonly, but not always, the first patient) in whom the particular disease was identified.

https://en.wikipedia.org/wiki/List_of_eponymous_diseases#Aut...

This is sourced by a link to the American Association of Medical Transcriptionists, which is not a body I’d heard of but I guess have some skin in the game when it comes to the intersection of medicine and grammar. https://www.mtstars.com/word-For-eponyms-AAMT-advocates-drop...