You will find that William and Grace spell there last name FERGUSSON, I searched the name with one "S" which didn't show up.
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NZ Electoral Roll 1928

Name: Grace Evelyn FERGUSSON - Married
1 Vivian St
District: Wellington, Wellington Central
Also:
- William John FERGUSSON - Labourer

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NZ Electoral Roll 1935, 1938, 1946, 1949

Name: Grace Evelyn FERGUSSON - House Wife
101 Coromandel St
District: Wellington, Island Bay
Also:
- William John FERGUSSON - Labourer
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NZ Electoral Roll 1954

Name: Grace Evelyn FERGUSSON - House Wife
101 Coromandel St
District: Wellington, Island Bay
Also:
- William John FERGUSSON - Driver
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NZ Electoral Roll 1957

Name: Grace Evelyn FERGUSSON - House Wife
30 Broadway
District: Carterton, Wairarapa
Also:
- William John FERGUSSON - Driver
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NZ Electoral Roll 1963

Name: Grace Evelyn FERGUSSON - House Wife
30 Broadway
District: Carterton, Wairarapa
Also:
- William John FERGUSSON - Retired
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NZ Electoral Roll 1969, 1972, 1978, 1981

Name: Grace Evelyn FERGUSSON - House Wife
108 Broadway
District: Carterton, Wairarapa
Also:
- William John FERGUSSON - Retired
- Charles RUSSELL - Retired
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