it does occasionally appear in places that I would expect to know “better” (papers and articles rather than blogs, etc.).
I’m not sure what you mean. The current standard is not to use the possessive. From here:
Many medical conditions and diseases have been named after a person; this type of name is called an eponym. There has been a long-standing debate in the scientific community over whether or not to add the possessive form to the names of eponyms. For quite a long time, there was no established rule as to which to use, but general usage decided which form is acceptable. So you saw both possessive and non-possessive names in use.
In 1974, a conference at the US National Institute of Health attempted to make a standard set of rules regarding the naming of diseases and conditions. This report, printed in the journal Lancet, stated: “The possessive form of an eponym should be discontinued, since the author neither had nor owned the disorder.”
From The CBE Manual:
It is recommended that the possessive form be eliminated altogether from eponymic terms so that they can be clearly differentiated from true possessives.