Board Thread:General Discussion/@comment-5576236-20140215022241/@comment-11051098-20141002221228

Or, as I came to think of after I posted my previous comment here - maybe there are Sternritters without letters, like more Sternritters than letters, and Yhwach didn't want to have more than one person have the same letter.

Or, as you say, Kubo forgot Shaz.