Name, date and place of birth, month/year and place of death, added here in April 2022, and from a post written by Brian Brandon about 'James George Cox' on "The First Four Ships" website:
http://www.firstfourships.co.nz/pics/othrppl.php?table=others&id=56
Brian Brandon is a x2 great-grandson of James George Cox, and being descendant through James' son, James George Coleridge Cox.
Brian of nzolivers is also a x2 great-grandson of James George Cox, but descendant through James' daughter Elizabeth Annie Cox.

Result from birth search on New Zealand BDM website in April 2022:
1853/2456. Cox, NR. Mother: Louisa. Father: James George

Full date of birth of 15 August 1853 confirmed from further searching in April 2022 on BDM Search by incrementally changing the date range for the birth.

A marriage search on New Zealand BDM website in April 2022 produced two possible entries. More research needs to be done:
1873/10990. Bride: Emmeline Seymour. Groom: William Cox
1872/4320. Bride: Sarah Jane Wilson. Groom: William John Cox

Result from death search on New Zealand BDM website in April 2022:
1879/657. Cox, William. Died age 26Y

Full date of death of 31 July 1879 from further searching in April 2022 on BDM Search by incrementally changing the date range for the death.

New Zealand Electoral Roll - Wairarapa Roll for 1874/75
Cox, William, Mataikona, household, Mataikona, house
Cox, James George, Place of Abode: Featherston. Qualification: (1) freehold, Featherston town sections Nos 308, 312; (2) leasehold, Mataikona 5000 acres [Father]

New Zealand Electoral Roll - Wairarapa Roll for 1875/76
Cox, William, Mataikona, household, Mataikona, house
Cox, James George, Place of Abode: Featherston. Qualification: (1) freehold, Featherston town sections Nos 308, 312; (2) leasehold, Mataikona 5000 acres [Father]

New Zealand Electoral Roll - Wairarapa Electoral Roll for 1876/77
Cox, William, Mataikona, household, Mataikona, house
Cox, James George, Place of Abode: Featherston. Qualification: (1) freehold, Featherston town sections Nos 308, 312; (2) leasehold, Mataikona 5000 acres [Father]
Cox, Samuel Stanley, Mataikona, household, Mataikona, house [Brother]

New Zealand Electoral Roll - Wairarapa Roll for 1877/78
Cox, William, Mataikona, household, Mataikona, house
Cox, James George, Place of Abode: Featherston. Qualification: (1) freehold, Featherston town sections Nos 308, 312; (2) leasehold, Mataikona 5000 acres [Father]
Cox, Samuel Stanley, Mataikona, household, Mataikona, house [Brother]

New Zealand Electoral Roll - Wairarapa Roll for 1878/79
Cox, William, Mataikona, household, Mataikona, house
Cox, James George, Place of Abode: Featherston. Qualification: (1) freehold, Featherston town sections Nos 308, 312; (2) leasehold, Mataikona 5000 acres [Father]
Cox, Samuel Stanley, Mataikona, household, Mataikona, house [Brother]

New Zealand Electoral Roll - Wairarapa Roll for 1879/80
Cox, William, Mataikona, household, Mataikona, house
Cox, James George, Place of Abode: Featherston. Qualification: (1) freehold, Featherston town sections Nos 308, 312; (2) leasehold, Mataikona 5000 acres [Father]
Cox, Samuel Stanley, Mataikona, household, Mataikona, house [Brother]

New Zealand Electoral Roll - Wairarapa Electoral Roll for 1880/81
Cox, Thomas William, residential, Mataikona, settler
Cox, Samuel Stanley, residential, Mataikona, settler
Cox, James George, Qualification: freehold, Place of Residence: Featherston; Occupation: settler; Featherston town sections Nos 308, 312 [Father]

New Zealand Electoral Roll - Masterton Roll for 1893
Cox, Thomas William, Te Mai, settler, residential
Cox, James George Coleridge, Te Mai, settler, residential [Brother]
Cox, James George, Te Mai Place of Abode: Featherston; Occupation: settler; Qualification: freehold; Mataikona, known as Te Mai, 600 acres [Father]