Ships always carry paper charts for areas of operation. Some waters, eg Indonesia, are non-WGS84 compliant which means electronic charts do not match reality. [Manual compensation can be achieved with complex nav equipment]
GPS is so reliable I've done many night passages around Australia's coast. The paper one below is a current Aus Hydrographic colour chart yet there are still many blue and white charts with soundings dating back to the late 1700's when surveys were carried out by James Cook and Matthew Flinders, among others.