Thanks for the replies.
Originally Posted by GUWonder
Maybe WLUSA2UK ?
Yes thats the one, for ORD-MAN.
I think you could be right in that it means that the fare might not be "upgradeable" to a more flexible fare / higher class of service even by paying.
I've only ever needed to use a gold upgrade voucher once before, in January, but I believe that it was a Q fare so have no direct comparison to make.
Thanks again