An update - as of August 10, when used to book reservations in California:

Cp559298 - gives 5%
Cp545949 - gives 5%
Cp545856 - Invalid/expired code
Cp559305 - gives 5%
Cp548389 - gives 10%
Cp540176 - gives 10%
Cp546071 - gives 10%
Cp566835 - not expired, but gives 0% discount

Cp550807 - gives 6%