This can be a state by state thing, my state association director said the "first" loss counts. Here are the scenarios and responses for tournaments only
1. Wrestler A is injured during the quarter-finals, but completes the match and ends up winning. He ends up defaulting to 6th place.
Result: The semi-final loss is taken on the record, but NOT considered a head to head victory for any of the default victories.
2. Wrestler A is injured in the semi-finals during a match during legal wrestling action and cannot continue, thus losing by default. He does not continue and defaults to 6th.
Result: The loss in the semi-finals counts on both wrestler's record, the losses in the consolations do NOT count on the defaulting wrestler's record. See more below.
3. Wrestler A is injured after an illegal move in the quarter-finals and wins via injury default. He proceeds to default to 6th place.
Result: A win on the wrestler's record for the quarter-final win, the loss also on the other wrestler's record. No other losses attributed to the wrestler who was injured. See more below.
In terms of if it counts as a head to head victory.
2. This is a tricky case, technically yes it does. However, good judgement should be taken into account. I was in a meeting where a kid lost on blood time with the score 0-0 and no more than a minute into the match. The losing wrestler was perceived to be better. The coach who won would not concede and wanted the higher seed. Unfortunately it did not help him. If the wrestler is winning and ends up losing you should take that into account and coaches who play the system like that are only hurting everyone else.
3. This should be considered a head to head victory. However, the winning coach can use good judgement in the case that the losing wrestler was better and there was no intent on injuring the wrestler.
As far as the scenario of advancing to the finals and "no-showing" that should count as a loss on the record, but not a head to head.