Originally Posted by
diburning
Yes, those have always been possible, but as I mentioned, there needed to be a Mint fare filed for the city pairs.
For example, when Mint first rolled out, Mint was only offered out of JFK (to LAX and SFO). However, I could book a Mint + Core connection on the same ticket, online, out of Boston at that time, because there were Mint through-fares filed between Boston and SFO/LAX. So, what I mean is, if there's a through-fare filed for a common logical connection, you can book it all on one ticket online. If you're trying to book between a city pair where they didn't "think of" filing a Mint fare for, then not even an agent can do it (piecing it together does not work).
I was specifically thinking of SEA - ACK. Until this year, it required purchasing to separate tickets, Mint to east coast and coach to ACK. At that point one either had to call to have a phone agent combine the tickets into a single itinerary for a fee, or have the agent at the airport do so at no additional cost (though took a while). I suppose that they must have recognized that connection a week ago as a valid Mint itinerary recently as my mother purchased a ticket being able to select mint to JFK and Coach to ACK herself, rather than being forced to buy two tickets, or call to upgrade to Mint on the SEA transcon.