Block Prints And Late Trade Reports

Most exchange trades hit the public consolidated tape essentially instantly, but large privately negotiated "block" trades, often arranged upstairs between two institutions away from the public order book, are typically granted a short reporting delay, on the order of minutes, before the broker-dealer must report the trade to the tape. This exists because immediately broadcasting a huge trade would let the rest of the market front-run the dealer's unwind of any resulting inventory risk, so regulators trade off transparency for a short window that lets the dealer manage the position.

The practical consequence for anyone reading the tape is that a "block print" appearing right now describes a trade that was actually agreed upon and priced several minutes earlier, at prices and conditions that may no longer be current. A trader treating a stale block print as fresh information, for instance inferring current institutional sentiment from a trade that was actually locked in well before the market moved, is working with a systematically lagged signal, and the size and direction of block prints are more useful as a record of recent large flows than as a live read of what is happening on the tape right now.