The combined airline today has about 473 A/C, 7,875 pilots. Since there are minimal retirements between the 2 airlines, someone hired today will need a few thousand pilots below them to upgrade, and this will have to come from growth or attrition since retirements are minimal. Let's say we got 200 new A/C. That'll require 3,300 additional pilots at the ratio of 16.5 pilots per A/C. Now we'd be a 673 A/C airline with 11,175 pilots. If nobody left, and nobody retired during the time it took to add 200 new A/C, someone hired today would then have 3,300 pilots below them. Still probably not enough to get that left seat. Obviously you could assume some retirements and attrition in your calculations, and multiple A/C types and several bases improve one's time to upgrade, but you get the idea.

How long would it take the combined airline to add 200 A/C, or grow by roughly 40%? NK is past it's massive growth phase, and our seniority lists are both fairly stagnant at the higher seniority levels.