A distance along the route
Route kilometre (RKM) describes distance along a route. The metric should include the relevant route boundaries, measurement method and reporting context.
Keep the stages distinct
Surveyed, mapped, executed and commissioned lengths are different measures. State which one is being reported and investigate differences against the same route or segment scope.
RKM is not positioning accuracy. Observation spacing and geographic accuracy also describe different things. Read planned vs executed RKM.