I'm pretty sure the death record is the right one as I have found the burial record for Frank on www.icc.govt.nz/ServicesA-Z/Cemeteries/CemeterySearch.aspx
It gives his last address as 66 Maitland Street. I checked the last letter from his wife and it was that address, not Duke Street, which must have been and earlier address for the family that I had but I will still send for the record so as to check that it is the right Frank Thompson next month(when funds allow)
I think its possible that the marriages for the children could be right as in the letter send in 1939 Harriet says that Frank Henry had been married for nearly 6yrs without any children and that both other two children are married with one son each.
thanks for the leads you have given me I will let you know of any progress I make.