I remember testing getRecentlyClosed couple of months ago, and I was getting duplicate results (as duplicate tabs, individually and one more time under window object) so I ditch it and continue to maintain the list of closed tabs per session manually.
And overall philosophy of this API is confusing.
Tabs with negative index are from previous session?
what would WindowId represent ?.. it's not id of the window in which tab is closed, because in my results all WindowId's are the same (and tabs are from different windows)
Chrome on hamburger menu is giving limited number of recent tabs? (I closed around 25-30 tabs, and only 8 is shown)