fair enough !
I have actually never tried to use points for upgrading. So, I will not be able to comment on this.
Well, that's not the entire truth... Twice I have wanted to upgrade with points, but have been upgraded due to overbooking in Y... Always from EWR.
In other cases I have been "upgraded" to Y+ (when flying A330 & A340) and not wanted to use points to upgrade to C - as you know, points can only be spent once...