There isn't going to be any issue if you don't either give airline details or give incorrect info. It's just easier to do it right from the beginning. I find that those that book without the correct flight info tend to start overthinking it...they start getting worried that something 'bad' will happen because DME doesn't have the correct flight info!
A month out and no flights yet?? You're a brave soul!!! Hope you get the flights you want! You'll have to let us know how it goes.