Call immediately after booking to straighten out fare classes. Keep notes including agent names. If you book straight W to claim an upgrade over the water, the web site is so egregiously stupid about these things that it will comply. W class will get you a seat in TK coach, but no mileage credit. Their letters do not correspond to United letters, yet specifying fare classes on United.com is a blunt instrument that will get you in trouble. So study the problem and call.

I was offered a few thousand miles for calling about this after the fact. I was thankful but stated that my primary motivation was to fix the system. They neither fixed the system nor gave me the miles. So be careful what you say in such situations. I never imagined that they'd fail to complete the offered deal, but this is United.