They could detect if the post is still getting significant search traffic, and if so, do the fact check.
Even before we knew about the Seattle choir, Twitter could have given the tweet a fact-check in the form, "Actually, there is conflicting evidence and we are not sure to what extent it is airborne." But of course on what authority does Twitter make that fact check? There are no easy answers.
Even before we knew about the Seattle choir, Twitter could have given the tweet a fact-check in the form, "Actually, there is conflicting evidence and we are not sure to what extent it is airborne." But of course on what authority does Twitter make that fact check? There are no easy answers.