Why only snippets of 19th century books on Google?

Google's blog has an explanation of their approach to copyright protection. What is peculiar is that large numbers of 19th century books indexed by Google's fabulous library project are displayed only as snippets, the way that they display copyrighted works. This is seriously hampering our project. Each time that we have contacted Google to point out that a 19th century book is erroneously displayed only as snippets, contrary to their policy, they refuse to correct the problem, and give the following response:

Thanks for taking the time to email us. Google respects the rights of copyright holders and the tremendous creative effort of authors. In order to keep within the bounds of copyright law, we abide by strict guidelines when determining whether a book should be held to be under copyright. We may display only snippets for books that are in the public domain if we can't verify their copyright status. Google Book Search is still a young program, and we're always improving it for our users.

We're puzzled by the response and have repeatedly asked for clarification, but Google declines to explain why.

This seems like a simple technical issue that could be quickly and easily fixed.