Jack there is no mention of a first marriage for Mary....no mention of the name HOCKING either.
Although I don't have any details on Henry's arrival in Australia his wife Mary arrived in Adelaide on the "Cressy" in 1847. She immigrated with her parents & siblings from Iddesleigh, Devon and was the 6th of 10 children and a sister of my GG Grandmother, Eliza Jane Gill. When Henry and Mary married, Mary already had a four year old son named John Henry Gill. .....................
Henry died in November 1874 at Tam o'Shanter Belt when he was only 39. Mary was widowed with 6 children .............she eventually remarried 3 years after Henry's death. Her second husband was a Charles or George Allington. George was a bachelor and 38 years old when they married in Port Adelaide. Although her second marriage lasted about 10 years she doesn't appaar to have had any further children. Mary died in July 1887 at Port Adelaide.
If Mary had married Thomas
HOCKING she would have been known as Mary
HOCKING when she married Henry
SHORT. Why was the birth reg of John Henry cross referenced....usual with illegitimate births.
The marriage of Thomas and May is on the SAGHS index
I have the resources you mention and cannot find a marriage for Mary
GILL to Thomas
HOCKING.
Mary's re-marriage
ALLINGTON Charles 38 years Status Single Father William ALLINGTON
SHORT Mary Ann 38 years Status Widow Father William GILL
11 Dec 1877
At the Manse, Port Adelaide PtA 113/874
Mary appears to have lowered her age when marrying Mr ALLINGTON
Death
ALLINGTON Mary
9 Jul 1887 53 years Status Married Relative George ALLINGTON [Husband]
Residence Port Adelaide Death Place Port Adelaide PtA 164/409
Death notice
http://www.rootschat.com/links/0m94/Only
ALLINGTON death in the same area.
ALLINGTON Charles
13 May 1889 53 years Status not recorded Relative not recorded
Residence Birkenhead Death Place Birkenhead PtA 178/439
Charles is buried at Hindmarsh Cemetery.
There is no headstone.
When you visit SAGHS you could have a look at this resource - Book and fiche - perhaps Henry is also buried at Hindmarsh.
http://catalogue.nla.gov.au/Record/2176910Cheers
Cando