We flew back to the US on 4 July, booked through Flights by Celebrity. It wasn't until about 5 weeks prior to that flight that FBC confirmed the return (FCO-MCO) half of our flights. Even then, one week later we were contacted directly by Celebrity HQs in Miami to explain that the flights selected did not meet Celebrity's requirements for time between arrival Civitavecchia and departure FCO. They did offer and confirm a good Business Class option and that flight, on America via PHL, was on time and very comfortable. Since you are schedule to fly more than 6 weeks from now suggest call FBC as well as email them requesting they provide finalized ticketing.routing. It will work and the cost benefit was worth it.
Do be warned: even with Business Class the check-in, immigration and security processing at FCO it took over one hour and a half. To make sure we arrived FCO with plenty of time before flight (which was on-time) we arranged for private transfer via Rome Cabs which as perfect.