Should a GLAM purchase an item of jewellery in 2023 attributed to an artist from Palmerston North who died in 1959. Is it correct that this doesn’t qualify for the royalty as the known maker died more than 50 years ago? 

Correct this is no longer a qualifying resale (assuming it would otherwise have been), as the right to a resale royalty for this Artist expired fifty years from the end of the year that they died, ie at the end of 2009.