When you make a seat change using OLCI it will not show up in your itinerary. OLCI is a different system than the reservations system.. I don't know what each is called internally but OLCI appears to be the system that is used by the agents at the airport.

Definitely nothing to worry about. In the future what you could do is change your seat using the seatmap function on your itinerary first, then do OLCI.