A bare selbri, with all its sumti vanished into zo'e-land, is called an "observative".
Some people seem to have been fooled, thinking that because this case is given a different name, it must follow a different rule than other cases. But in fact, the zo'es of an observative are filled in from context in exactly the same way that all other zo'es are filled. There is nothing special or different about observatives except for the name.
mi'e jezrax