Support Board

In general we never rely on the timestamps provided by an exchange to indicate time of trade as it usually does not have good enough granularity and it usually is not representative of the time of the matching event and is subject to change.
We timestamp data to indicate when we received the messages and it could be argued that such a time is a better time as it actually represents the first time we could know about it (we presume that we could know about it when someone else outside the exchange could know about it).
The fact that orders were matched at some time is probably not as important as when the rest of the world found out about it so they could take action on it.