I find that very strange.
I would be interested to know why that is.
Were all of the coins of that period destroyed by later kings?
Were all of the coins of that period carried off by foreign conquerors?
As traders wo traveled for years at a time, the tendency would be for older coins to leave and newer coins to be used domestically.
If the coins were mainly gold and silver, all the more so as they were the universal coin of trade for centuries.