Coins that were produced close to the time of burial would generally be present in the greatest quantity (and be less worn). The oldest coins would be found in lesser numbers and would be more worn.
If there is at least one coin in the hoard whose date is firmly established then the date of deposit (i.e., burial) must at least be after the known date of that coin.
The burial date is likely shortly after the time of the latest coin.
Further, it would generally be expected that there would be no "gaps" (i.e., no absences of coins over a long period).