I may be way off, but I seem to recall (from FewMiles?) that R also covers upgrades from full Y, as well as another upgrade to Business as well... others will likely have a better answer. I do see the C0 - it means no seats remain allocated for VIP / mile upgrade from Coach to Business. It may be they never allocated any, and it may be they will allocate more, IF yield suggests it. But IMO, you are SOL on C for FCO... Try some other dates, since flexibility is often the key to using VIPs / miles to upgrade (as opposed to paying a few thousand more dollars...)

You likely know this, but if you click on a fare basis letter designator, a popup will give you an abbreviated list of the different fare first letter designator (because there are variations... I upgraded April and May flights bought in L, but the entire fare basis code is actually LLW30AR,) to C inventory using VIPs, after scoping it all out on ExpertFlyer. The C inventory showed as everything from C2 to C7 on the flights I booked.