True, except for patients age 55+. They did not receive the initial half-concentration dose. That's almost certainly why those receiving the half-concentration dose experienced much higher efficacy (90% vs 62%) — they were younger and had fewer co-morbidities.

No, the mistake is not showing additional promise. The “mistake” is a clue that the study was completely botched.

Not completely botched, they approached the regulator with an error and followed their advice on how to continue. The regulators advice was how the final results were presented in the published paper (i.e. with the accidental dosing as a separate group).