Joseph – thanks for the explanation – that makes sense! Not sure what the answer is… it’s a good question.
I would guess that if you write Motzei Shabbos, you should follow up with the previous week’s Parsha since it’s Motzei Shabbos of last week’s Shabbos. On the other hand if you were writing the date, you would write the next weeks’ Parsha (but in that case, you probably wouldn’t mention the Parsha anyhow).