Changes made after award, such as change orders, also become contract documents. The agreement lists exactly which documents count.
Example: a note on a plan sheet conflicts with the spec section. The contract may state which document governs. Many contracts tell the contractor to ask the architect.
Know what is in and what is out. Bidding requirements, the soils report and your own proposal may not be contract documents unless the agreement lists them. If your exclusions matter, make sure the subcontract includes or references your proposal.