This is correct. These companies will sell you a promised section then figure out how to get the tickets later.
The best time to shop for tickets is closer to the season and game. People will hold them until the last minute hoping for a big payday, then drop the price when the deadline to ship or transfer runs out, sometimes resulting in less than face prices. If it's not a huge game (ie Georgia), there will be tickets available, but you have to be patient.