Theoretically it should be ticketing at any time prior to departure for J and F, however most of the partners reserve the "right" to set their own deadlines. This is what may be occurring in your case - if the booking has a SSR from one of the carriers involved in the itinerary requesting ticket numbers by a certain date, that deadline is extended to the entire itinerary. SQ in particular are becoming notorious for early, sometimes very early, ticketing time limits when booked in restricted booking classes or where flights are showing heavy advanced bookings.

From issue 04/08 29FEB08 -
5 ADVANCE RESERVATIONS/TICKETING:
Note that the following carriers may apply ticketing time limits for booking classes shown below:
AC / BD / CA / LO / LX / OS / OZ / SK / TP / TG / SA / SQ / UA / US