The dates that lied
Dispatch_Date arrived in two formats at once. Most rows were ISO — "2026-05-31" — but a stubborn minority were text-month: "31-May-2026". No flag marked which was which. Parse the whole column as ISO and the text-month rows fail silently, dropping out of every transit-time calculation and making the network look faster than it really is. Parse it the other way and the ISO rows break instead. The fix was disciplined, not clever: detect the format row by row, normalize everything to ISO, and reject anything that still refused to parse so nothing failed in silence. A short Power Query step — and every duration built on top of it became trustworthy.