How to mark/unmark as N/A

To imply the actual unavailability of data in the eCRF and to distinguish it from data currently missing to be entered at a later time, the data point can be appropriately marked as “not available”.

For example you might have the information that a medication has been stopped, but you know already you will never receive the actual stop date. You mark it as not available to confirm it is not missing or pending, but cannot be provided.