Although what you've posted is technically correct, I have seen enough posts to keep me a sceptic. There are reports about KF members who entered non-SQ FFP numbers, saw them on their bookings (even at check-in) but yet still found after the flight that SQ changed them so they credited to KF instead! and then they had a great deal of trouble (some times unsuccessfully) getting them re-credited to the correct program.

It would now seem that to make my booking and use the benefits of the SQ website I'll have to give up my barge pole.

BTW.
I did bring this to the attention of SIA Customer Services and was told, that the KF member would have to contact the SQ reservations offfice after the booking was made in order to credit to another FFP.