Thanks, Peter.
I will let you know how things work with the Costco/Hyatt certificates.
The printed conditions look pretty clear, and we are Plat with Hyatt. BUT, if we have a problem, we'll get a refund from Costco & write some letters to Hyatt. I'm guessing we will be better off in the end if some jerk gives us a hard time. But it *should* work easily.
