Currently the date range in the search wizard is based on the First Date field. The users should be able to choose which date field they want the range to be based on. This could either be via a dropdown within the search itself or at the Model level.
Clients have data that come into the system on different dates, when they perform a search to pull back approved match group items they return one half of the match, but not the other due to a difference in First Dates.