…. (see post in pearl blog)
[1] with the latest FX rate applied.

At time 140+3x, the same execution msg could be “enriched” then routed to the FX dealer. The dealer earlier gave a quote of USD/JPY of 100.50/1 to the exchange, and the exchange marks up to 100.00/99. Now the trade is already executed in a Japanese exchange to buy a stock for JPY 1 mio. The US broker needs to pay for it by selling USD. As market taker, broker sells USD at the “worse” price of 100.00. Between time 50+x and 190+3x, the dealer may have a new FX rate, but let's hope dealer can accept the earlier rate.

In this flow, the Japanese exchange makes money by buying USD (from broker) at 100 and selling (to bank) at 100.50. JPY amount is fixed 1 mio.

This is all trade execution time, not settlement time. At this stage, exchange, broker, and FX bank need to record the trade prices, in order to settle latter.