Finally... I got my email invitation and I've got:

You’re all set to earn up to 5,000 bonus StarpointsŪ with Your World Rewards™ on eligible stays of two or more nights from 1 October until 31 December 2017.

Book and complete your first stay to earn 2,000 bonus Starpoints.
Earn 1,000 bonus Starpoints on your second stay.
Then earn 2,000 bonus Starpoints on your third stay.
This bonus offer is in addition to the Starpoints you’ll earn for each eligible stay.

I have the stays already booked so free 5000 points to me.

Interestingly, my friend who I induced into SPG got the double nights a couple of weeks ago which will get him to Platinum for 2018 and he also got a second invite and got these additional points just now. Anyone else get two offers?