Greetings from Maine. The Co-op has been around for at least 15 years. Maybe I can answer some questions too. No, the bid is awarded to a primary vendor. Members may have a secondary vendor.
Individual districts resolve day to day problems.
However, a report for is sent to the co-op quality control chair. She and the co-op president have frequent meetings with the distributor to handle any recurring problems. Yes, based on each district's individual preference. One mandatory meeting is held in August. During the year that we are generating a new bid, the number of meetings increase.