While a spiky rate of growth in the number of back links may be a factor used by search engine 125 to score documents, it may also signal an attempt to spam search engine....
Just to throw out some thoughts for consideration... were the patterns of link growth to the sites in question far enough outside normal patterns to have been flagged as "spiky", thus prompting further tests?
And were there any patterns in the "shuffling" or traffic observed that might suggest what Google was trying to measure? Any stats on visitor engagement with the site during the times of the test? Was Google trying to evaluate, eg, whether the notoriety the site was receiving was based on wide appeal or on heavy duty promotion?
I feel like we approached these by-the-book.
Possibly, the definition of "by-the-book" could be changing.