The old needles certainly show some kind of stress. It could be a cast, as you mention, and/or trouble with the roots due to poor soil. I can’t tell for sure what the problem was.
The new needles look so good (they look great!) I would hold off on treatment for now. I’d also be curious if others in your area have needles that exhibit similar symptoms. If so, the trees might be suffering the same thing. (DC area enthusiasts: is needle cast a significant problem for black pines?)
In the meantime, it’s about time to remove the old needles at which point the tree should look fantastic