The "medical forfeit" got added this season to address this.

1) Injury default technically requires both wrestlers to report and the clock to start.

2) Medical forfeit does not require either wrestler to report to the table. The forfeiting wrestler may continue to wrestle in the tournament.

In the "old days," injury default was a "catch all" usage, especially during finals of subregionals or strategically during regionals. It technically didn't follow the rules (as people would Inj Def well in advance), but nobody enforced it.