This was a very enjoyable read. I built a nearly (architecturally) identical system a few years back that also had to be scrapped for different reasons. This brought back a lot of memories. The sanity checks, the index reconstitution issues, dealing with the insanity of security identification and tracking through time. The fun cases are the ones where it's not even clear what the right answer truly is, e.g. company…
Also, this was really my first time with equities - my professional trading career was derivatives-focused - both listed (CME) and OTC (FX forwards/swaps). I think I lost the first few months simply trying to reorient my style of thinking.
Water under the bridge I guess.