I agree, collecting a lot of Pacific Islands coinage, you get used to mintage figures of like a few thousand up to maybe a million pieces at most for some dates. I think mintage size fits with population. 600k for a Guernsey coin is quite high as the island only has a population of 25k now, and likely much less in 1968.
In New Zealand, most predecimal coins had mintages in the 7 figures and 6 figure mintages for the rarer dates. Our rarest circulation coin had 40,000 minted and its a scarce collectible (1935 3d). But in 1961 they minted a halfcrown with just 80,000 minted, yet the coin is quite cheap, mostly as it only circulated for a few years and its a base metal coin.

A true rarity - 5 figure mintage coin, few know or care about.
I actually get more of a buzz of low mintages from countries with a larger population like Canada. Several dates of silver 50 cent coins had extremely low 5 figure mintages like 1905, 1934, 1948 and these coins are definitely harder to find than say a Samoan 20 sene coin of 1967 which had a mintage of 50,000.
Or with my Australian collection - some super rarieties include the 1934/35 Victorian Centenary Florin. The coin had a mintage of just 75,000 when usual Florin mintages were between 1 and 8 million coins per year. However this coin was sold at 3/- (50% mark up) and given it was the depression, few were saved. Needless to say the coin became a rarity and 21.something k were minted leaving some 53 and a bit k left. Yet compare that to the 1927 Parliament House florin, 2 million minted, no mark up and issued in 1927 during the height of the roaring 20s. These coins go for melt value or even less.

Another popular rarity is the 1938 Silver crown, first issued in 1937, the large silver coin was a huge flop and some 1 million were issued, a low but not rare mintage. In 1938 just 100k were minted and these are truly scarce (Costs are in the mid 3 figures, but not super rare like a 1930 penny). Even more scarce are the specimen 5 shilling banknotes they were going to issue in 1939, but got interrupted by the war.
I love coins. Especially silver, gold and anything really old.
Member of the Royal Numismatic Society of New Zealand and the Auckland Numismatic Society