I have spent a bit of time over the last two weeks looking at resources from the local library. NZRLS over a number of years have published some working timetables of the NZR network and they do contain a lot of detail that can be useful for various purposes. However except for a list of track telephones in an appendix of the timetable they don't list actual route mileages for each route, only for a timetable section. For example from Frankton to Taumarunui the mileage will be shown only starting from Frankton and for going the other way it will be shown from Taumarunui. In other words the actual milepeg measurements from wherever the zero peg of the line are not shown.
There is enough mileage detail for me to be able to reconstruct the mileages by putting in the numbers into a spreadsheet or I could actually rely on one of the original imperial editions of the Quail Atlas but I do prefer to use NZR official sources rather than a third party source known to have inaccuracies.
There are as it happens some other sources like over the years I managed to obtain way and works district maps showing the extents of each way and works district and these do show how the mileages ran on each line and also show many of the stations.
One of the frustrations of the NZRTA is that you do have these gaps because I don't know how they got their mileages in cases where there had been a deviation or realignment but they seem to have managed with stations that must have been closed in 1974 when metrication took place for which there was no metric measurement. The fact is that because we can get an imperial mileage in most cases from the old WTT, we can work out the actual distance from the next nearest station or stations that was open and go from there.
OK here is an example, the mileages for the stations on the old NIMT through the middle of Palmerston North are not shown in the Quail 4th edition. Even showing them in imperial measurements would be OK. Or the mileages on the old Rimutaka line which I have been mapping lately. Using the WTT data I now have I can put in miles-chain measurements for these stations which will appear in the maps because that's the way it should be. However it will be decimal miles to avoid the confusion over the decimal point in the official WTTs not representing actual decimal measurements.
Upper Hutt 32.40 km (old measurement 20.24 M, or 19.46 M via the old route up the western side of the Hutt Valley)
Cross Creek +17m42ch
Pigeon Bush +20m54ch
Longburn 81m24ch from Wellington in 1947
Palmerston North 84m79ch
Terrace End +1m56ch
So it can be seen it should be really easy to get all the mileages if you have an old enough WTT and it should be possible to have complete measurements on all my maps.