Traditionally that's what's recommended but I don't know whether that's what actually happens. In the last decade, for 90% of the years, there have been more codrivers than drivers participating in a given year. And since 2000, there have been about 33% more codrivers than drivers participating. If everyone was sticking with getting experienced codrivers, than there would be fewer codrivers than drivers, as new drivers would come and go but the experienced ones, by definition, would be sticking around.
I think we have a lot of double novices in the cars... but that's a good poll! I'll make it over on NRS.