What you may be forgetting is not growth or stagnation, but potential shrinkage. The combined DAL/NWA list shrank by over 2,000 or so from the merger until now. Historically, a merger has never been 1+1 = 2, but rather something less due to contract productivity "enhancements" and route overlap efficiencies.
A simple search of the NWA/DAL Seniority List Integration award shows 12434 pilots on the combined list.
Another quick, & seemingly simple search of the current (Nov. '13) seniority list shows 11653 pilots.
A difference of 781 pilots. Where, may I ask, are you getting the numbers for the statement which I bolded above?