I've just been denied all elite benefits and stay credit at the Westin Warsaw due to the stay having been booked by Carlson Wagonlit, which is the only way my company (80.000+ employees) has been booking stays for years. I've asked their reservations department for clarification, but if these stays indeed fall under the "third-party bookings" rule, then I'm definitely moving my 40+ nights a year completely away from Marriott.