Reissues (no matter what type of change, e.g., date/time, so long as it involves a monetary exchange with NW, i.e., change fee) are required. Reissues are processed in a queue by the reissues ticketing department based on date of departure.

Case in point, we had to change my SO's return trip next month. The change was made the first week of March. The itinerary was finally reticketed last week! So it can be awhile before NW gets around to reticketing you ticket.

If you're really worried.... call Northwest and ask them to "force ticketing". The agent will have to manually call the ticketing department and have them do it for you. It's up to the agent's discretion, so YMMV.