I used to be a photographer and have stared at the lens group diagrams from many a lens manufacturer, so take this with a grain of salt: In a lens there are multiple lens groups, it's often that the aberration correction is its own distinct group, with fixed input and output groups flanking it. I'd imagine that the distance to the projection surface, in this case the next lens group, can be fixed and thus distinct from the distance to your ultimate subject. A fun fact is that Helmholtz reciprocity says that regardless which direction light passes through an optical system you can reverse the distortion and reconstruct the input signal.
