They're often sent together, yes, not always. An insertion order is a description of what the advertising is in a general sense. Where we might have multiple insertion orders, we then put them into one invoice, or sometimes they're the same.
Evidence of meeting #113 for Access to Information, Privacy and Ethics in the 42nd Parliament, 1st Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was know.
A video is available from Parliament.