Looking at a chord towards the end of the development in measure 169, beat 2, spelled C♯-E-A♭ over the G pedal.
How would you analyze this in the context of the harmonic progression at that point?
The best I can come up with is that the C♯/E is a non-harmonic tone leading up to D-F-A♭, a diminished chord with subdominant function. So the core of the progression is then V-ii(dim)-♭VI-V.
What I'm wondering about is whether the C♯/E/A♭ has a function of its own in the progression. I might call it a ♭ii(dim) but that doesn't quite feel right.