The expectation that all import errors would exist/persist as batch committal exceptions does not apply to the scenario described in this Knowledgebase article.
This series of events occur when you have mapped an import field to a simple data list with a collection of possible values and your source file contains invalid entries for that collection. (e.g, a State field is mapped and the import file is populated with value, such as "ON", which does not exist in the CRM States code table collection).
The import process reads in the string value of the content in the import file (e.g., state = "ON") and compares it to what exists in CRM (states code table). When this occurs for an invalid value such as a state = "ON," an import error will occur because the value supplied did not exist in the States code table collection in CRM. The resulting batch is created with no value entered into the state field. (Since the value didn't exist in CRM, it was discarded when the row was added to an exception batch.) The exception batch does not have a batch row error matching the import can be committed because there is no logic in the committal process to prevent a commit for a blank state field, only to prevent invalid data.
Thus, the best way to prevent this scenario is to create import files that do not have invalid data, such as a value for state that doesn't actually exist in CRM.