I can't speak for Bersarin, but I do think that, overall, the uncollected stuff is usually stronger than most unpublished stuff. For The People Look Like Flowers at Last, Martin culled most poems off early little mags. Posthumous doctoring aside, the poems in The People might be stronger because they were largely uncollected then --rather than unpublished.
When I was putting together Storm, I re-read everything unpublished and uncollected, and I picked some 400 poems that I found strong enough to be published: 300 of them were uncollected, 100 unpublished.