Actually I just found this story in the guardian from 2000:

http://www.guardian.co.uk/Archive/Article/0,4273,4042964,00.html

The most important part for me is this:

"The threatening letter from Harbottle and Lewis received a polite but firm reply from Kövesi's publisher, Mike Gorman of M&C Services, requesting proof that Robinson genuinely owns the copyright to Clare's unpublished works. This has been met with six months of silence.
Kövesi is now preparing his second "unauthorised" edition, John Clare: Flower Poems, which will be published in October. "Until clear proof is offered that the copyright claim is legitimate," he says, "I will continue to publish Clare in accessible and easily available editions, and I would urge others to do the same."

I'm gonna go find out whether my Penguin Selected has any overlap with the Curtis Brown editions (these are the 'unpublished' poems you're talking about).

But frankly the fact that this article is from 2000 leads me to think nobody should worry too much about what setting any John Clare poems.