diff --git a/skills/librarian/SKILL.md b/skills/librarian/SKILL.md
index af7dc0c..800b90b 100644
--- a/skills/librarian/SKILL.md
+++ b/skills/librarian/SKILL.md
@@ -214,8 +214,9 @@ As part of each maintenance loop:
 
 ## File Conventions
 
-- All filenames: **kebab-case** (`alex-chen.md`, not `Thomas Owen.md`)
-- People files: `firstname-lastname.md` (or `firstname.md` if unambiguous)
+- All filenames: **kebab-case** (`alex-chen.md`, not `Alex Chen.md`)
+- People files: `firstname-lastname.md`; if last name unknown, use
+  `firstname-unknown.md` as a placeholder (never bare `firstname.md`)
 - Date files: `YYYY-MM-DD.md`
 - Decision files: `YYYY-MM-DD-topic.md`
 - All files are markdown