2) They would just end up being off every week if they took such a blind approach.
1) I disagree. It makes far more sense as any marketing research company/resource needs to make sure its numbers are credible in order for them to be taken seriously. Better to adjust to the official numbers than to stubbornly stick to less accurate in-house extrapolated numbers.
2) But they're ALREADY OFF every week if offiicial numbers are to be based on. And in this regard by a statistically relevant amount. It's better to adjust into the official numbers, that way you'd at least be right for the week the number is announced and then extrapolate going in further using official numbers as the basis in order to reduce the size of the error going forward.