Monty's right. It's important for the poor stude to see what it's like as -2 and -3, so he knows where he fits into the sequence for formation changes and the like. If he crashes, then refer to him by his individual callsign, as per the slides and the auth sheets, to avoid any ambiguity.
The front line would be mad to renumber, but a basic 3-ship teach is something else entirely. I applaud front line practice filtering down to the training system, but doing away with renumbering at BFJT "because the front line don't do it" stuck me as a bit silly. The front line don't do it, but they're not teaching basic, academic formation!