Mat Piscatella has written in twitter:
"Eh, late note for the release, but Nintendo Switch hardware drove the highest unit sales for a September month since the PlayStation 4 in September 2014. Great month for Switch."
I understand it as less than PS4-Sep-14 (538k) but more than PS4-Sep-18 (421k).
421k < NSW < 538k
Not very accurate but that is what we have.