It really depends on what equipment the aircraft has. A lot of classics have been upgraded, but there are still some flying with units such as the Delco Carousel which only has the ability to accept nine manually inputted waypoints at a time. The ones I flew had Marconi FMS900s fed from Litton 92 IRSs and glass instruments. Those FMCs were actually better than the 744s.
If you're using the older types of kit, yes it can be a bit of a challenge. Cross checking every waypoint is essntial. But I can't believe there are many aircraft still flying with those. Modern RNP requirements demand better in some parts of the world. For example, European RNP requirements state you have to have a Nav display.