While I agree, it wouldn't have helped. The first n sign-ups per commit worked. So the problem didn't manifest during the day, only when they stopped committing

While I agree, it wouldn't have helped. The first n sign-ups per commit worked. So the problem didn't manifest during the day, only when they stopped committing. Now granted, if they'd carried on doing stuff (but not redeployed production) it may have shown up in say mid-aftenoon, or not depending on volume. And of course the general guideline of not deploying anything to production early in the day, or on Friday, is still valid.