I have been thinking about this for years now and never put much gray matter into it. You send a proposal to customer and then you should lock in a snapshot to preserve the details of that quote so you can always revert or reference it. Waiting to generate a revision until a change is needed opens up the project to human error where someone could go make changes to the project and send another PDF proposal without creating a rev before making their changes and you may not have a way to ever get back if you are omiiting info from your PDFs for confidentiality/competition reasons. So best practice is to create the Rev each time a PDF is sent.

In that case, it makes sense to me that the notes area on the dialog box for creating the rev should be amended for to the previous rev that was just sent to the customer and not the current rev.

Is everyone else doing it this way where you generate a rev each time you send a proposal or are we the exception?

I don't know why I didn't suggest this earlier; good one. A general note for the original rev of the project can be added when creating the project, then every revision note is for that new revision.