After the ticket has been purchased, you should also be able to look it up using the ticket number (starting in 006 for DL ticket stock). I've found that careful NW/DL elite agents and good travel agents document all PNRs for you as SOP and tell you all of them on the phone when you make a reservation or purchase a ticket.

However, why not get a FF account? It's free, quick, and easy. Or is the problem that you're crediting a different airline's FF program for the trip? (Very wise.)