I just registered successfully for the following offer after following the link, although I may have previously received and ignored the offer:
"Eligible members can earn double elite qualifying nights and stays on all eligible paid stays at any of the more than 1,500 hotels and resorts in the SPG® program from March 1, 2018, through May 31, 2018 (the “Promotion” and the "Promotion Period"). Only SPG® Members invited to register for the Promotion via spgpromos.com/selectmemberexclusive are considered eligible for this Promotion (“Eligible Members”). Furthermore, Eligible Members must register between February 15, 2018, and April 30, 2018, 11:59 p.m. ET (the “Registration Period”) for this Promotion. Stays and nights consumed prior to the date upon which the Eligible Members register for the Promotion (the “Registration Date”) may not be applied to this Promotion. A list of hotels and resorts participating in the SPG program can be found at spg.com/terms under section 1.2.
A "stay" is a stay of one or more consecutive nights at the same SPG Participating Hotel by an SPG Member who (A) provides his/her SPG Member number at the time of reservation or at check-in; (B) pays an eligible rate; and (C) stays in one of the reserved guest rooms. If an SPG Member checks out of a guest room and then checks back in to a guest room at the same SPG Participating Hotel on the same day, it will count as a single stay for purposes of calculating stays.
An “eligible stay” is a stay with at least one (1) eligible paid night at any of the over 1,500 hotels and resorts in the SPG program, paying an eligible paid rate during the Promotion Period. An “eligible rate” is any rate that is eligible to earn Starpoints® in the Starwood Preferred Guest® program. Free Night Award stays and Cash & Points stays are not eligible toward this Promotion. Hotels and resorts in the SPG program can be found at spg.com/terms under section 1.2. A description of Eligible Stays and Eligible Rates can be found at spg.com/terms under section 2.1. An SPG Member may only earn Starpoints, Eligible Nights and Eligible Stays for up to three guest rooms during any Eligible Stay if he/she stays in one of the reserved guest rooms and pays an Eligible Rate for all of the guest rooms. Please note that certain prepaid rooms where the booking is made through a third party (including but not limited to travelocity.com, expedia.com and booking.com) are not Eligible Rates and do not earn Starpoints or qualify toward promotional earnings.
The bonus elite-qualifying nights that post to the member's account as result of the Promotion will not count toward SPG Lifetime™ status nights requirements or toward achieving any milestones required to obtain any other SPG Promotion Rewards including, but not limited to, for example, Status Challenges, Bonus Starpoints and Free Night Awards. Members upgraded to elite status solely as a result of the bonus elite-qualifying stays or nights posted will not have a year of elite status count toward SPG Lifetime qualification, unless the member achieves the typical required stays and nights needed for elite status. This offer is nontransferable and may not be combined with any other stay or night acceleration offers."