Like, the ending events took up far less space that you remembered. This can be influenced by how you revise. I always find things that need to go in, and so the second draft ends up fatter. Comparing how far I got through the expanded version to how far I have to go in the still lean version is misleading.
It can still be surprising.
To be sure, it raises question of exactly how monstrously long this monster is going to turn out to be. . . .