Why would the shift to a new methodology bias the estimates to one end? I would expect a new methodology to make comparisons of data between the two systems to potentially be unhelpful, but I wouldn't expect a valid methodology to bias one way or another.

Related, I wouldn't expect past data to bias a current estimate. If 6 or 12 months of positive growth biases the next prediction it falls into the hot hands fallacy. It isn't predicting based on current predictions, its predicting based on recent past behavior and extrapolating forward. This only makes sense to do if the data is not yet available, and even then the extrapolation isn't a useful estimate of current conditions.