The Collaborative International Evaluated Library Organisation (CIELO) Pilot Project, working under the auspices of the WPEC Subgroup 40 (SG40), was established to generate complete evaluations for a selection of the most important isotopes for parameters in nuclear technologies: U-235, U-238, Pu-239, Fe-56, O-16 and H-1 with the aim of improving the accuracy of the data and resolving previous discrepancies in the overall understanding. The CIELO Pilot Project has been overseeing numerous activities, which recently resulted in an entire special issue of the Nuclear Data Sheets journal (Issue 148, 2018) being dedicated to the subject. It has also led to the production of a suite of new nuclear data evaluations that have been incorporated into major nuclear data libraries. The outcomes of evaluations include significant harmonisation of discrepancies between independent programmes, improvements in the performance of international standard nuclear criticality and neutron transmission benchmarks, complete uncertainties for nearly all parameters and the use of modern data storage technologies. Overall, this work has leveraged considerable, parallel and experimental work in collecting improved experimental measurements to support nuclear data, while highlighting high-priority areas for further study. A productive and durable framework for international evaluation was thus established to build upon lessons learnt. These lessons will continue through new WPEC groups and a new International Atomic Energy Agency (IAEA) evaluation network, which was initiated in response to the success of the NEA CIELO Pilot Project.