What's loaded in the FMC is what the operator has purchased. There are obviously numerous 'modules' that are loaded up according to what the operator pays. Sometimes you find the database incomplete. It is not unknown to fly to a new destination and find the arrival airfield is not even loaded, let alone the STARs and SIDs. One then has to hash up what information you can. Not common, but smaller airlines operating to a wide range of airports can experience this. Indeed, capabilities of FMSs can vary according to the modules loaded into the computer, so we certainly don't assume everything is loaded!