one more note (not quite closed yet): I now have Oscar Robert Sunnerdale's death certificate. He was definitely buried 14 Sep 1923 South Brisbane, as was the Robert Sunnerdale buried with my Harriet. I believe it was the same person. Reuben Robert, his son (only child listed), was the informant and gave Oscar's birthplace as Landskrona, Sweden. By the time of his death Oscar Robert was 70y, had been in Qld about 22y and was a night watchman, but before that in the Australian Electoral Rolls he was a mariner 1905 and 1908 in Maryborough, and in 1913 in Oxley Division in Brisbane. He had married in Maryborough, 1900 from Qld bdm. It seems his wife Mary Anne, from Qld bdm and the Trove article above, died in Maryborough in 1912 and then he must have moved to Brisbane.
The mystery of the connection remains though. Harriet had children both in Maryborough and in Brisbane.
I think I need to look at Maryborough hospital records, if they are somehow accessible, for Thomas Butler in 1884 and Mary Anne Sunnerdale in 1912.
Thanks for all your previous help.
