I think those valuations are based on people over valuing their stuff, same with the rarity numbers, when coins listed as unique proofs or worth 6 figures, seem to be owned by 0.9% of Numista members.
No veracity checks are made when people add their coins and some of it may be simple mistakes, entering your coins in the wrong column. I have been caught out a couple of times (Everytime I made an accident, as I am always honest or are trying to be, as according to my ability, but I have bad eyesight and keyboard skills and make mistakes), I will always correct my mistakes.
I use Numista to reference coins, but NEVER go on their prices beyond bullion or face value of a piece.
Bertrand list an Average/Fine 1933 NZ Halfcrown at $18, but that was before the massive silver price rise this year.
Most NZ pre 1947 silver coins are graded as Ave/Fine for all coins between Good (The worst possible usually) to Fine (Decent) and then VF is twice as much and the coins get rare in EF and higher. Same for early (1947 - 1955) Cupronickel, but most 1956 and later coins except errors and varieties are quite cheap in all grades but UNC.
NZ Bronze coins, Average condition is VF as few wore beyond VF (The worst I have seen are 1940/42 pennies in Fine or good Fine condition). A VF bronze coin is usually brown and no lustre, but the hair is sharp on the King and there is clear wear on his cheeks and the breast of the Tui.
Many 1951 and later bronze is easily found with some lustre (Except the rarer dates of 1954 and 1955, and 1956 Strapless penny).
Basically pay those prices no mind.
Here is my price estimate for 1933 and 1934 Halfcrowns
Good/VG/Fine - Melt value only (About $24 per coin), VF around $40, EF $100 (Many high VF coins are around $60), AU $250, UNC $400.
These are very old and likely need refining
I love coins. Especially silver, gold and anything really old.
Member of the Royal Numismatic Society of New Zealand and the Auckland Numismatic Society