Erinn Clark, Jérémy Bobbio (Lunar) and Ximin Luo told Debian the story comes from 2 friends.

The Die Zeit article suggests the 2 friends are Isis Agora Lovecruft and Alison Macrina.

https://www.zeit.de/kultur/2016-08/jacob-appelbaum-rape-sexu...

Enrico Zini introduced the words "first-hand accounts", making it appear that 3 more victims exist when maybe there is only one or none.