Exploratory search is an uncertain endeavor. Quite often, people don’t know exactly how to express their information need, and that need may evolve over time as information is discovered and understood. This is not news.
When people search for information, they often run multiple queries to get at different aspects of the information need, to gain a better understanding of the collection, or to incorporate newly-found information into their searches. This too is not news.
The multiple queries that people run may well retrieve some of the same documents. In some cases, there may be little or no overlap between query results; at other times, the overlap may be considerable. Yet most search engines treat each query as an independent event, and leave it to the searcher to make sense of the results. This, to me, is an opportunity.