Analysing Sociolinguistic Variation Book

I can hardly add anything to Christopher's excellent review on this book. It is really convincing that these parallel structures in the European languages are due to century-long language contact rather than shared retentions from the proto-language(s) or parallel developments. A notion I had some problems with, however, was the idea of "minor use patterns" being present in languages prior to the contact scenario, which then are turned into "major use patterns" through contact and grammaticalization processes. Maybe I missunderstood something, but this hypothesis seems to suggest that no new grammatical patterns could arise in a language if there hasn't been a minor and similar grammatical use for the element in question in the older stage of the language. That seems to be true for all cases discussed in the book, but doesn't strike me as a neccessary universal in contact-induced pattern replication. Gotta discuss this with my colleagues...
But nevertheless, this is a great book and will probably help me indeed seeing the big picture for my PhD thesis.