All suggestions are good and valid suggestions.It is a good idea to have some naming conventions setup for your team. Contract ID will always be unique and easiest way to search. That said in the upcoming 14s Sourcing release we are redoing the search architecture and along with an incredible performance increase we are also changing keyword search to be a generic search box that will search all fields and all documents based on the data input into the fields.
This will be release in the first half of 2015.
Leslie Martensen