I may be wrong but to the best of my knowledge Starwood has to date run two sweeps for SPG Amex referral bonuses: the first posted on Christmas Day and the second posted on March 5.
Hopefully they have at least one more sweep coming as I referred 4 FT'ers that supposedly (hopefully) used my referral code and reported back to me that actually they received the card, I had one referral bonus post in Dec and two posted yesterday so at the moment one bonus is still missing in action.