You'll also see comments like "I neck size until they're a little snug so then I use a body die (or FL die) to squeeze them a bit so they chamber smoothly again." What this indicates is from firing to firing the fit of neck sized brass to the chamber does evolve.
The reason Cortina and those guys FL size is so the brass fits the chamber the same way every firing. In the super accuracy/precision realm consistency is the name of the game.
