You're misunderstanding a little, although it's exactly what you think. The 2.7K recordings are not at all a random sample of the 400K, they were probably chose

You're misunderstanding a little, although it's exactly what you think. The 2.7K recordings are not at all a random sample of the 400K, they were probably chosen because the labels could find a reasonably clean copyright history for them (i.e. be pretty sure they actually owned them.) The "small sample" is the number of those 2.7K that have gone out of print. They're playing language games to imply that almost all of the music that is part of the "Great 78s" project is currently in print by only suing over 0.7% of it, and saying that most of that 0.7% is available as a digital download. So to summarize, they combed through an IA project, and probably found that it consisted 99.3% of recordings that the entire RIAA (which represents the entire mainstream US recording industry) doesn't think that it can prove ownership of. These, they insist, are just cover so they can distribute the 0.7% of Bing Crosby 78s.