Inside the anthology, each book will show completion status on the title page.
The anthology metadata doesn't have that. In part, because I don't know a way for the anthology metadata to usefully store and display that information.
My best idea would be to add it to anthology Comments when "Include Books' Comments in Anthology Comments?" is checked.
At that point, would it be worthwhile adding a user configurable template for building anthology Comments?
Is that something people would find useful? A template for the HTML included for each book in anthology comments?