fortunately, i'm not too familiar with changing names on a ticket, but even if it was the travel agent's fault, honestly, you should have caught it by now, as other posters have suggested.

no offense, but if i booked a "once in a lifetime trip" in november via a travel agent, i would most certainly have double checked the tickets as soon as they arrived, whether via email or regular mail. the fact that you're just now reviewing the itinerary for mistakes, whether departure, arrival, flights, hotels, cruises, etc. almost 5 months after you booked it, doesn't sound that "once in a lifetime" to me.

while this may not help your original question of chaning your name 5 months after you booked the ticket, perhaps next time you book travel of any kind, you will go over the tickets with a fine toothed comb as soon as they arrive.

the best suggestion i can give is to review the terms and conditions of the tickets of the entire itinerary, and see if there is a "no name changes" clause. if that's the case, then call the agent or relevant airlines and cruise lines and see if they will give you some leeway. better to know now than to arrive for departure and be turned away.