The headstone reads 22/1/1951
The Births, Deaths and Marriages website says 23/1/1950
Their database says 22/01/1950

They checked the burial register at the archives ‏(PNCC 2/11/1 Volume 3)‏ which only gives the burial date 25/1/1950.

It indicates that the headstone had "new ledger and lettering. Fisher 10/6/53"

They checked the Manawatu Standard for the death notice which confirmed the 23/1/1950

Therefore I am going with the BDMH and Death notices being the most accurate.