If only cases never grew, you could neck size forever and there wouldn't be a need for FL or bump dies...
But they do grow. Eventually.
The key is to resize the case "just enough" to establish fairly easy chambering. Too much resizing sets up excessive case stretch near the head, which leads to case head separation. (Dangerous)
And then you can resume neck sizing.
Until the necks split.
My understanding is you can generally get quite a few reloadings out of a case, like perhaps 20, if you don't use maximum loads and if you take care to not overwork the brass.
Some guys believe in annealing the necks, to prolong case life.
(If this stuff was simple, it wouldn't be as much fun...
)