upside down noon

Our Mesorah has nine times a נון הפוכה (upside down letter נ) in תנ"ך. Twice in Bamidbar 10:35 (ויהי בנסוע) and seven times in Tehillim. The last Rashi in this week's Parsha writes that  "- הנון הפוכה " At the end of the Parsha we have an upside down נון In our מסורה both The Aleppo & The Leningrad Codex,(before Rashi) there is no נון הפוכה at the end of  Parshas נח. The בית יוסף יו"ד ס' ערה quotes from the רשב"א that our Sifrei Torah are kosher even though we have no נון הפוכה. The קסת הסופר writes that today if a Sefer Torah has a נון הפוכה  at the end of Parshas Noach, we should not use it.