If you want to be a stickler for the rules as far as the word count goal for NaNoWriMo, then you wouldn't count the paragraphs of the story towards the 50k if they were written in October. Does that mean you can't use them? Nope. You don't know at this point how long the first draft will become until you've gotten to those last words.

Let me use some personal examples since I do this often.

I've had first drafts range from 23,000 to 170,000 (No, I didn't write 170k in one month but umm close, 160k NaNo crazy year). I've also done a couple of years for the official month or camp nano events where instead of starting something new, I tried to finish stuff I already had started since I've got like 5+ novels started at any given time.

Usually, the counts for NaNo and the sprints are done in the moment. So, whatever gets written during November is what counts towards those totals. However, elements written at other times can be used in the novel. I've even rewritten short stories I've created on WDC for contests that were scenes for novels once I got around to actually writing them. So, the general aspect was there but I still did all new words.

There are options. If that makes sense.