When I was a PoG TL I actually had the chance to talk to some of the people doing this job.
One of their MAJOR gripes was that stock position and item size would change after the vendor gave it. For example, the glittery Elsa doll shows the box dimensions as 3Wx10Hx1D and hanging, but it arrives at the store and the box is actually 2 inches deep and doesn't have hangtabs, so it jacked up the capacity and the fit.
After my time at Target I worked for another retailer doing store remodels and one of my roles involved interfacing with the planners, their solution was to set every pog after building it in a fake store. After it was built and stocked they made adjustments and fixed it, then the fixtures were pallet wrapped and just shipped to a local store, store just rolled them out pre stocked.
Never had a problem with pogs in that company. Perfect fit every time.