[kragen]

Yeah, inventing a thing in one time period is mutually exclusive with adopting it from people who invented it in an earlier time period.

The author of the book to which the Google Books link linked also had a doctorate, in chemistry; WP describes him as "a key figure in the fields of history of science and chemistry in the beginning half of the 20th century" and "the first president of the Society for History of Alchemy and Early Chemistry". He probably knew more about the history of soap than Dr. Janega, but she might know things about it that hadn't been discovered when he died, and probably knows more about the social context of its medieval use than he did. Is your mention of Google Books intended to suggest that Google Books might be falsifying the text?