Yes but a lot of the times base choices don't matter that much. Frequently they'll just throw the entire class in ORD, MSP or DEN regardless of what you bid for. At least one more bid will usually close while you're still in training so you have a second shot at getting what you want. There's a lot of movement on the bottom right now so people haven't had much trouble getting into the more junior bases on either airplane. If your base choice is something like SEA, PDX, PHX, SFO (on the RJ) you're not going to get it regardless of your last 4 digits.