If the document behind the overlay is not shown on another image in the same batch, index as much as you can see.--
Does this mean to include that information on the same entry, or to create a new entry?
It depends, if the overlay is about the same individual as the document underneath it, then you could combine the information into one entry. If it is about two different individuals, then you would have to create another entry.
It's always best to share your batch to get a great answer. The instructions for that can be found by clicking on the third icon from the right in the horizontal toolbar.