I'm currently assembling parts to build a tribute Rick. I measured a friend's two 4001's. A 2016 4001S midnight blue, and a fireglo 1974. Without going into too much detail here, the bodies are very different, the '74 has the aforementioned and nicely exhibited here, larger body. The wood working on the routs, is absolutely awful. I have photos that show it, but trust me, it's bad. The rest of the craftsmanship is totally alright.
The weird routing is hidden under the pickguard, bridge pickup frame and bridge, so most folks would never know. The 2016 instrument has really nice routing, fit and finish.
What I found even more interesting, is the difference in the body THICKNESSES. The '74 body, is 1-5/16" and the newer 'S is a sixteenth thicker at 1-3/8" !
A personal note: The pickups are all visually identical- the neck and bridge pickups in both basses are the 'button' type. They are the 'high gain' in the 'S.' I LOVE the sound of the new 'S' model, and I do not care for the sound of the '74 at all! Yes, they both have that familiar Rick sound- but the 'S' has a much better tone, especially with both pickups on full. Amazing how two similar basses can sound so different.