Actually, the stuff in the store has usually been in warehouses for long periods of time. During that time, they lose nutrients.

Some, probably vitamin C. But that can be recouped with produce that always has lots anyway, e.g. tomatoes.

Not just vitamin C. B vitamins can be reduced by up to 70%. There is degradation with many other nutrients as well.

"Up to" doesn't paint a realistic picture, but it's a moot point. Nutritional deficits in the West are a result of poor consumption choices, not the lack of nutrition in produce.