Final answer:
The duration of the validity of a letter of approval from the board for instructors depends on the board's policies, which is not specified in the provided information.
Step-by-step explanation:
The question pertains to educational administration, particularly the validation period of a letter of approval from the board issued to instructors. Given the context provided, it appears that the board issues this letter to instructors who meet certain approval criteria, typically when a new curriculum is to be implemented or there is a significant change within an educational department. Although the blank in the question is not filled in, such letters commonly have validity periods that are at the discretion of the issuing board. If the curriculum change mentioned is to take effect in June, the letter of approval might be valid for the upcoming academic year, though the exact duration would be set by the board's rules or policies.