I surmise that what was "lost forever" was only a copy of the documents. I base that on common sense, as well as this from the linked article (about the Pentagon Papers):
> So Mr. Sheehan smuggled the papers out of the apartment in Cambridge, Mass., where Mr. Ellsberg had stashed them; then he copied them illicitly, just as Mr. Ellsberg had done, and took them to The Times.
(Of course, I could be the one that is confused here, misreading this discussion. But I don't think that is the case)
Yes, it was Ellsberg's copies of the nuclear strategy documents that were lost. The original documents were still in a classified safe in the Pentagon. Some were later declassified, long after they were obsolete, and probably some have never seen the light of day.
I surmise that what was "lost forever" was only a copy of the documents. I base that on common sense, as well as this from the linked article (about the Pentagon Papers):
> So Mr. Sheehan smuggled the papers out of the apartment in Cambridge, Mass., where Mr. Ellsberg had stashed them; then he copied them illicitly, just as Mr. Ellsberg had done, and took them to The Times.
(Of course, I could be the one that is confused here, misreading this discussion. But I don't think that is the case)