Applied multiple RUCs; Why are some flights coded RY and others SU?
 

Multi-city trip coming up with RUCs applied. Two flights are coded First Class, RU and three are just SU. Called the Diamond line and the agent sees all as RY. Although the RY flights have the option of selecting seats, when I try it won't let me. Do I believe the agent? Do I need to keep calling? Flights are not until October.

What classes of service are offered on these flights? Are they all domestic with regular FC, not marketed as business class and with no D1 service?

Something is wrong then. SU is the free medallion upgrade to C+. All should show RY or OY. Sounds like 1)ticket hasnt been reissues and 2)reservation hasn't been properly changed for upgrade. Till it shows RY/OY you don't have a confirmed seat in F.

If the flights are within the upgrade window, OP could have received free elite upgrades on some segments and RUC/GUG upgrades on other segments. Of course, the free elite upgrades should have happened only for segments for which use of the GUC/RUC was not requested, but a good agent might have noticed that free elite upgrades were available for a portion of the itinerary and grabbed those seats rather than leaving the OP to hope that the GUC/RUC supported upgrades clear.