POWO follows these authorities in synonymising this name:
Govaerts, R. (1999). World Checklist of Seed Plants 3(1, 2a & 2b): 1-1532. MIM, Deurne. [Cited as Coprosma grandifolia.]
Govaerts, R. (2003). World Checklist of Selected Plant Families Database in ACCESS: 1-216203. The Board of Trustees of the Royal Botanic Gardens, Kew. [Cited as Coprosma grandifolia.]
Also see: https://onlinelibrary.wiley.com/doi/10.1002/tax.12993
and: https://onlinelibrary.wiley.com/doi/full/10.1002/tax.13151 (連結)