Final answer:
Materials added to a contract are known as addenda before it is signed and as amendments after it has been executed. Addenda provide additional information, whereas amendments modify the existing terms of the contract.
Step-by-step explanation:
Materials added to the initial contract can either be described as addenda or amendments. An addendum typically refers to additional information or documents that are added to the original contract before it has been signed by all parties. On the other hand, an amendment usually refers to a change or modification to the terms of the contract after it has been signed.