That is unacceptable; Kimpton's Facebook page clearly says it's valid until 9/29. I would escalate this to their social media rep, either here, on Facebook or on Twitter.
Kimpton Hotels & Restaurants - Facebook
July 21
It's back! The secret social password is alive and well today through Sept. 29th. Just say "Summer of Karma" at check-in and receive a special surprise from the hotel.
Where will you use the secret word first?
I have stays in the Bay Area this weekend and fully expect the properties to honor the promo.