They should have done max(old_score, re_score) for all test takers. That's the only fair way. Although I don't know if SAT grades on a curve, which wouldn't play well with this method (I think?).
1. You can't award a bonus question to a subset of people, that is not a fair way of running a standardized test. You can't score some people as x/154 and some at x/153.
2. The old score was just plain wrong, so using it in any way is unfair.
The truth is no one got that question right because there was no right answer available. None of those available answers is "righter" than the other so it is not fair to assign a higher score to one of them like you proposed. Those people that got a higher old_score also got that question wrong, so their old_score is as wrong as any, and awarding them this unearned extra point would be unfair.
The only two fair options would be: to annul the whole test and make everyone retake; or the one taken where they annul that one question pretending it never existed and score based on the remaining questions (with each remaining question now being worth a fraction more). And this later option is in fact very fair, I don't think there is any real argument against this being fair.
It does suck that people were initially informed a wrong score and then later were disappointed with their real score. On this line I find it absurd that the SATs don't have the recourse period before they release the scores, and instead just releases the tentative scores as if they were real. This would all have been avoided if they heard the recourse and annulled the question before publishing results (as pretty much any serious exam around the world does it).
