Each round of negotiations involves a series of trade-offs; some excellent proposals will be advanced, and some excellent proposals will not make it to the final round. The difficult decisions made at each stage take into account likelihood of success, cost, and what may benefit the greatest number of members. Sometimes it's a critical item that may only impact a small group of members, but will do so profoundly.
Generally, bargaining team members focus on supporting the decisions made at the bargaining conference. Each round of bargaining offers different challenges, and the group must weigh each proposal against the desired outcome and what happens during the course of face to face negotiations.
If a round of bargaining is likely to be very focused on wage and benefit increases, the team may decide (for example) to forego pushing for other costly gains that might diminish the likelihood of the employer accepting desired wage increases.