Mark previously written text as “new” for purposes of Session Target

This post is subsequent to a question I asked in the tech support forum:

My wish is that there be some way to mark selected text as “newly entered” from the point of view of Session Target updating.

It is currently the case that Manuscript Target and Session Target differ in how they count words. The former counts all the words in, e.g., the compile group, whereas the latter limits words to those newly entered. This is very nice when writing a new manuscript, but works less well when editing one.
I am currently using Scrivener with NaNoWriMo, with a goal of “Edit X Words”. My process is to copy sections of my manuscript from a folder containing a copy of my previous draft into the Manuscript folder and editing it there.
The Manuscript Target works appropriately, since it counts everything, and at the beginning of a session, the Session Target is useful to know how many words to aim for in the session. However, since the session count only counts new words, it is not useful as a scale for my progress in editing. In fact, the session target count could even go negative if I mostly delete.

If there were a way to mark text or files as newly written, then Scrivener’s session target would be as useful when editing manuscripts as it is when writing them.

Thank you,
Greg Shenaut