Final answer:
The hearsay exception for a statement that was once known but is now insufficient is the Recorded Recollection. It is used when a witness's memory about an event is no longer reliable but they previously recorded their memory when it was fresh.
Step-by-step explanation:
The recorded hearsay exception for a statement that was once known but is now insufficient is the Recorded Recollection exception. This exception applies when a witness has made a record of something they once had personal knowledge of, but now cannot recall well enough to testify fully and accurately. The record must have been made or adopted by the witness when the matter was fresh in their memory, and it must accurately reflect that knowledge. The record can then be read into evidence, but it may not be received as an exhibit unless offered by an adverse party.