Drew For example, if I purchase a point to point for a train at 10:38 A.M
You cannot buy a point-to-point ticket for a particular train. Such a ticket is always for a route. So you are never limited to the train you selected.
In the past when buying tickets online or at the ticket machine all you needed to enter was the origin and destination, and the date. Only recently have the railways started by first showing you a schedule, that you pick a train out of. But once you have picked a train you will be offered the different ticket types that are relevant for your selection.