You forgot NumStolen, NumPickedUpAndDroppedElsewhere, and NumEatenBySquirrels. Shrinkage is relentless.

If the world were a deterministic computer system, yes.

It is not.

For instance, NumIn would indicate how many received at the store, no? But what then?

It needs to physically exist somewhere. The display? Overflowing onto the overhead? Overflowing onto the next overhead over? Pushed to the back of the overhead behind something else? Kept in the back because there's no room anywhere?

For 10,000+ different products or so per store.

Stolen, moved around in store by customer, put in the front special deal display..

A lot of stores used to do things like close for part of a day to do inventory. I assume there is still some syncing up during the night or whatever. But I also assume that, as with many things, many stores have probably been willing to trade off a degree of accuracy for reduced costs.

They still do, but it usually only happens a few times per year.

NumStolen, NumScannedAsOneThingButActuallyAnother, NumLost...

And numStolen.