Effectivity data shows the conditions under which an item is effective.

In the standard system, time effectivity is defined by the Valid-from and Valid-to dates.
You can display this data directly from the item overview.

An item that has been changed with a change number whose effectivity is defined by an effectivity type (parameter effectivity), has no Valid-from or Valid-to date on the item overview.

You can only display the effectivity data indirectly, by displaying the change master record. By double-clicking on the field Change number in the change master record you goto the item overview.