Why do single character searches return unexpected results in Vault?
Vault does not utilize "starts with" searching on single character searches due to the potential performance impact.
For example, searching for 'N' would not return a document titled "New Sales Report". To get around this, users can search for more than one character. Searching for 'Ne' would return document "New Sales Report" because Vault does utilize "starts with" searching when a user searches for more than one character.
Vault Help Documentation: About Document Search Results