Addendums vs. Amendments

These two distinct contract processes function as follows:

An amendment is typically used to change something that’s part of an original contract. Think of amendments as modifications to the earliest agreement (for example, altering an agreed-upon deadline).

An addendum is used to clarify and add things that were not initially part of the original contract or agreement. Think of addendums as additions to the original agreement (for example, adding a deadline where none existed in the original version).

Source: Adobe