thanks for posting this, an interesting bit of history.
Being from the UK, I’m unfamiliar with the term “paper-road” and gravel roads rarely exist. In England & Wales, hundreds of miles of unsealed legal roads are available but they are known as “by-ways”, many of which are thousands of years old as they were built by the Romans or Medieval drovers moving cattle / families across the land. Although not as old, it seems the paper roads in NZ are equivalent.
In England, there is much opposition by walkers, horse riders and cyclists against the use of vehicular access & councils often decide to ban motorised traffic as it means less maintenance costs (usually a local farmer is paid to maintain them).
Consequently, there is much secrecy about the legal by-ways for vehicles & although an OS map may imply access, it may not necessarily be open to vehicles. Therefore, most off-road bikers join the Trail Riders Federation to discover where and when by-ways can be ridden.
In Scotland almost all the land is private so there are very few legal by-ways or unsealed roads.