au-half-sovereign-1918
Museums Victoria holds one of these and photographs each one, which is a documented proof that a coin bearing this date exists. It says nothing about how many were struck, and is not counted as a mintage anywhere here.
What they hold: circulating.
Coin - Half Sovereign, Western Australia, Australia, 1918 circulating
No mintage figure is recorded for this issue yet.
It does not tell you what the coin is worth. A catalogue can honestly report how many were struck, what metal is in one, and what the documents say. It cannot report a market price without either inventing it or copying someone who might have. So this catalogue reports the first three and stays quiet about the fourth.