What is the ruling on advancing Zakat from an existing Nisab if the advanced amount covers two years but is drawn partially from other wealth?

Primary text

If the owner of forty sheep (the Nisab for sheep) advances two sheep for two years, and one sheep is from the existing forty and the other sheep is from wealth not yet considered part of the Nisab, the payment is valid only for the first year. It is not valid for the second year because the initial required Nisab (forty sheep) has been depleted to thirty-nine sheep, thereby falling short of the required threshold for the second year. If the Nisab is later completed, the ruling on the advance payment for the second year must be reconsidered based on the completion date.