In the course of looking at some stuff around Dunedin I have found Retrolens now has aerial photography from 1942, and also the 1960s and what appear to be official NZR surveys from 1972.
1960s coverage varies. Year 1960 coverage is not for the whole railway network in Dunedin, while 1967 coverage is at a lower resolution.
The official 1972 surveys seem to be the best bet of getting anything from earlier than 1978, and crucially for my interest, they do include the old Dunedin locomotive depot, which must have been almost closed. As I already have 1978 it will make for an interesting comparison.
So then I expect to add the 1942, 1972 and 1985 or 1986 coverage which is what is available, to the 1978 that I already have.
There is no particular timeframe for completing these at this stage.