What's July 31st?
This is from the terms
" SPG® members must register online at spg.com/selectmemberexclusive8 by 11:59 p.m. Eastern Time (ET) by July 10, 2015. Registered members can earn bonus Starpoints® for every eligible stay between June 1, 2015 and August 31, 2015 (the “Promotion Period”) at all participating Starwood Hotels and Resorts."
really strange! I registered with the link you posted and here are my terms:
Eligible member must register by June 30, 2015, 11:59 p.m. EDT. Member can earn 1,500 bonus Starpoints® after one (1) eligible paid stay, 2,500 bonus Starpoints after the second (2nd) eligible paid stay, and 3,500 bonus Starpoints after the third (3rd) eligible paid stay. As part of this promotion, member may earn a maximum of 7,500 total bonus Starpoints for three eligible stays from May 1, 2015, through July 31, 2015 (the "promotion period"). This promotion is not transferable. Bookings made prior to the promotion period are eligible, but only eligible stays consumed during the promotion period will earn a bonus.