How can I determine if a client took possession of the Digital Delivery?

Tracking of Digital Deliveries is done from within the same tab they are sent. The recipients are displayed at the top along with the status (queued, sent, received, error). "Received" means the client has created their free account and taken possession of the video or collection.

Hovering your mouse over the status of that recipient will show a timestamp of when that status changed. This can be used to determine when the delivery was sent or the client took possession and first viewed the project.

If the "Distribute" permission was granted and the recipient has delivered the content to others, upon hovering over the status it will also show how many people to which they distributed.