Dean2 . . . .
If a handloader only reloads their belted cases one time, then you are correct. They should NEVER experience a resizing problem when loading belted magnum cases. However, most handloaders really hate that option, and I'm one of them. Sometimes new products come along that actually work very well.
My patented Belted Magnum Collet Resizing Die and Digital Headspace Gauge are good examples
With the right modern equipment, belted magnum cases can now be reloaded as many times as non-belted calibers.