Wat is Start-of-day position, trade-date position, settlement-date position?

The start-of-day position is the position a day begins with: the previous day’s end-of-day position, reconciled. The trade-date position counts every execution from the moment it trades; the settlement-date position counts it only from its settlement date (one business day later in US equities, Book 1, chapter 5), which is what custody and cash reflect.