So, for the pooled sections, the materials, whether textbooks or OERs, have to be decided by the discipline and cannot be changed by the instructor, right?

For pooled sections, the required materials are decided by the discipline and and must be used by the instructor in a meaningful way within the course. If a course is designated a Zero-Textbook Cost course and no specific OER materials are listed, the instructor may use any no-cost OER materials.