[Karst]

See here:

http://eil.com/products/rolling-ston...go-256905.html

It tends to be referred to as a CD-R acetate. Lot of artists tend to produce these as promos these days as test-pressings aren't really needed anymore. Considering the Nirvana aspect mentioned above here is an essay about it:

http://www.livenirvana.com/pr3/testpressings/info.html

So I would say the above discs come straight from the master which would make them 1st gen.