From my experience, SQ will make you wait till the very last minute before they give you an F boarding pass (award or upgrade travel).

If you don't get it you can complain to LH, esp if you dished out the miles for an F ticket.

SQ dreams that a large party will shell out full fare unrestricted F for their entire cabin. This has happened before (in the Asian boom days late 90s but a lot less now) but as long as F is empty they will give you a seat, just not right away.